Pennsylvania's history of human habitation extends to thousands of years before the foundation of the colonial Province of Pennsylvania in 1681. Archaeologists believe the first settlement of the Americas occurred at least 15,000 years ago during the last glacial period, though it is unclear when humans first entered the area now known as Pennsylvania. There also is open debate in the archaeological community regarding when ancestors of Native Americans expanded across the two continents down to the tip of South America; possibilities range between 30,000 and 10,500 years ago. Meadowcroft Rockshelter contains the earliest known signs of human activity in Pennsylvania, and perhaps all of North America, including the remains of a civilization that existed over 10,000 years ago and possibly pre-dated the Clovis culture. By 1000 CE, in contrast to their nomadic hunter-gatherer ancestors, the native population of Pennsylvania had developed agricultural techniques and a mixed food economy.

By the time European colonization of the Americas began, at least two major Native American tribes inhabited Pennsylvania. The first, the Lenape, spoke an Algonquian language and inhabited the eastern region of the state, then known as Lenapehoking. It included most of the state of New Jersey and most of the Lehigh Valley and Delaware Valley regions of eastern and southeastern Pennsylvania. The Lenape's territory ended somewhere between the Delaware River in the east and Susquehanna River in central Pennsylvania. The Susquehannock, who spoke an Iroquoian language, were based in more western regions of the state from New York in the north to West Virginia in the southwest that included the Susquehanna River all the way to the Allegheny and Monongahela rivers near present day Pittsburgh. European disease and constant warfare with several neighbors and groups of Europeans weakened these tribes, and they were grossly outpaced financially as the Hurons and Iroquois blocked them from proceeding west into Ohio during the Beaver Wars. As they lost numbers and land, they abandoned much of their western territory and moved closer to the Susquehanna River and the Iroquois and Mohawk tribes located more to the north. Northwest of the Allegheny River was the Iroquoian Petun, known mostly for their vast tobacco plantations, although this is believed to be complete fabrication. They were fragmented into three groups during the Beaver Wars—the Petun of New York, the Wyandot of Ohio and the Tiontatecaga of the Kanawha River in southern West Virginia. South of the Allegheny River was a nation known as Calicua. They may have been the same as the Monongahela culture and little is known about them except that they were probably a Siouan culture. Archaeological sites from this time in this region are scarce.

In the 17th century, the Dutch and the English each claimed both sides of the Delaware River as part of their colonial lands in America. The Dutch were the first to take possession. By June 3, 1631, the Dutch had begun settling the Delmarva Peninsula by establishing the Zwaanendael Colony on the site of present-day Lewes, Delaware. In 1638, Sweden established the New Sweden Colony, in the region of Fort Christina, on the site of present-day Wilmington, Delaware. New Sweden claimed and, for the most part, controlled the lower Delaware River region (parts of present-day Delaware, New Jersey, and Pennsylvania) but settled few colonists there.

On March 12, 1664, King Charles II of England gave James, Duke of York a grant that incorporated all lands included in the original Virginia Company of Plymouth Grant plus other lands. This grant was in conflict with the Dutch claim for New Netherland, which included parts of today's Pennsylvania.

On June 24, 1664, the Duke of York sold the portion of his large grant that included present-day New Jersey to John Berkeley and George Carteret for a proprietary colony. The land was not yet in British possession, but the sale boxed in the portion of New Netherland on the West side of the Delaware River. The British conquest of New Netherland began on August 29, 1664, when New Amsterdam was coerced to surrender while facing cannons on British ships in New York Harbor. This conquest continued, and was completed in October 1664, when the British captured Fort Casimir in what today is New Castle, Delaware.

The Peace of Breda between England, France and the Netherlands confirmed the English conquest on July 21, 1667, although there were temporary reversions.

On September 12, 1672, during the Third Anglo-Dutch War, the Dutch re-conquered New York Colony/New Amsterdam, establishing three County Courts, which went on to become original Counties in present-day Delaware and Pennsylvania. The one that later transferred to Pennsylvania was Upland. This was partially reversed on February 9, 1674, when the Treaty of Westminster ended the Third Anglo-Dutch War, and reverted all political situations to the status quo ante bellum. The British retained the Dutch Counties with their Dutch names. By June 11, 1674, New York reasserted control over the outlying colonies, including Upland, and the names started to be changed to British names by November 11, 1674. Upland was partitioned on November 12, 1674, producing the general outline of the current border between Pennsylvania and Delaware.

On February 28, 1681, Charles II granted a land charter to Quaker leader William Penn to repay a debt of £16,000 (around £2,100,000 in 2008, adjusting for retail inflation) owed to William's father, Admiral William Penn. This was one of the largest land grants to an individual in history. Penn proposed that the land be called New Wales, but there were objections to that name, so he recommended Sylvania (from the Latin silva: "forest, woods"). The King named it Pennsylvania (literally "Penn's Woods") in honor of Admiral Penn. The younger Penn was embarrassed at this name, fearing that people would think he had named it after himself, but King Charles would not rename the grant. Penn established a government with two innovations that were much copied in the New World: the county commission and freedom of religious conviction.

What had been Upland on what became the Pennsylvania side of the Pennsylvania-Delaware Border was renamed as Chester County when Pennsylvania instituted their colonial governments on March 4, 1681. Penn signed a peace treaty with Tamanend, leader of the Delaware tribe, beginning a long period of friendly relations between the Quakers and the Indians. Additional treaties between Quakers and other tribes followed. The treaty of William Penn was never violated.

Between 1730 and when it was shut down by Parliament with the Currency Act of 1764, the Pennsylvania Colony made its own paper money to account for the shortage of actual gold and silver. The paper money was called Colonial Scrip. The Colony issued "bills of credit", which were as good as gold or silver coins because of their legal tender status. Since they were issued by the government and not a banking institution, it was an interest-free proposition, largely defraying the expense of the government and therefore taxation of the people. It also promoted general employment and prosperity, since the Government used discretion and did not issue too much to inflate the currency. Benjamin Franklin had a hand in creating this currency, whose utility, he said, was never to be disputed. The currency also met with the "cautious approval" of Adam Smith.

The University of Pennsylvania in Philadelphia was founded by Benjamin Franklin in 1740, becoming one of the nine colonial colleges and the first college established in the state and one of the first in the nation; today, it is an Ivy League university ranked among the best universities in the world. Dickinson College in Carlisle was the first college founded after the states united. Established in 1773, Dickinson was ratified five days after the Treaty of Paris on September 9, 1783, and was founded by Benjamin Rush and named after John Dickinson.

James Smith wrote that in 1763, "the Indians again commenced hostilities, and were busily engaged in killing and scalping the frontier inhabitants in various parts of Pennsylvania." Further, "This state was then a Quaker government, and at the first of this war the frontiers received no assistance from the state." The ensuing hostilities became known as Pontiac's War.

After the Stamp Act Congress of 1765, Delegate John Dickinson of Philadelphia wrote the Declaration of Rights and Grievances. The Congress was the first meeting of the Thirteen Colonies, called at the request of the Massachusetts Assembly, but only nine colonies sent delegates. Dickinson then wrote Letters from a Farmer in Pennsylvania, To the Inhabitants of the British Colonies, which were published in the Pennsylvania Chronicle between December 2, 1767, and February 15, 1768.

When the Founding Fathers convened in Philadelphia in 1774, 12 colonies sent representatives to the First Continental Congress. The Second Continental Congress, which also met in Philadelphia (in May 1775), drew up and signed the Declaration of Independence in Philadelphia, but when that city was captured by the British, the Continental Congress escaped westward, meeting at the Lancaster courthouse on Saturday, September 27, 1777, and then to York. There they and its primary author, John Dickinson, drew up the Articles of Confederation that formed 13 independent States into a new union. Later, the Constitution was written, and Philadelphia was once again chosen to be cradle to the new American Union. The Constitution was drafted and signed at the Pennsylvania State House, now known as Independence Hall, and the same building where the Declaration of Independence was signed.

Pennsylvania became the second state to ratify the U.S. Constitution on December 12, 1787, five days after Delaware became the first. At the time, Pennsylvania was the most ethnically and religiously diverse of the thirteen colonies. Because one third of Pennsylvania's population spoke German, the Constitution was presented in German so those citizens could participate in the discussion about it. Reverend Frederick Muhlenberg acted as the chairman of the state's ratifying convention.

For half a century, the Pennsylvania General Assembly met at various places in the general Philadelphia area before it began meeting regularly in Independence Hall in Philadelphia for 63 years. However, events such as the Paxton Boys massacres of 1763 had made the legislature aware of the need for a central capital. In 1799 the General Assembly moved to the Lancaster Courthouse.

The General Assembly met in the old Dauphin County Court House until December 1821 when the Federal-style "Hills Capitol", named for Lancaster architect Stephen Hills, was constructed on a hilltop land grant of four acres set aside for a seat of state government in Harrisburg by the son and namesake of John Harris, Sr., a Yorkshire native who founded a trading post in 1705 and ferry on the east shore of the Susquehanna River. The Hills Capitol burned down on February 2, 1897, during a heavy snowstorm, presumably because of a faulty flue.

The General Assembly met at a nearby Methodist Church until a new capitol could be built. Following an architectural selection contest that some alleged had been "rigged", Chicago architect Henry Ives Cobb was charged with designing and building a replacement building; however, the legislature had little money to allocate to the project, and they dubbed the roughly finished, somewhat industrial Cobb Capitol building complete. The General Assembly refused to occupy the building. Political and popular indignation in 1901 prompted a second contest that was restricted to Pennsylvania architects; Joseph Miller Huston of Philadelphia was chosen to design the present Pennsylvania State Capitol that incorporated Cobb's building into magnificent public work, finished and dedicated in 1907.

James Buchanan, a native of Franklin County, served as the 15th U.S. president and was the first president to be born in Pennsylvania. The Battle of Gettysburg — the major turning point of the American Civil War — took place near Gettysburg in July 1863. An estimated 350,000 Pennsylvanians served in the Union Army forces including 8,600 African American military volunteers.

The politics of Pennsylvania were for decades dominated by the financially conservative, Republican-aligned Cameron machine, established by U.S. senator Simon Cameron, later a United States Secretary of War under President Abraham Lincoln. Control of the machine was subsequently passed on to Cameron's son J. Donald Cameron, whose ineffectiveness resulted in a transfer of power to the more shrewd Matthew Quay, and finally to Boies Penrose.

The era after the American Civil War, known as the Gilded Age, saw the continued rise of industry in Pennsylvania. Pennsylvania was home to some of the largest steel companies in the world. Andrew Carnegie founded the Carnegie Steel Company in Pittsburgh and Charles M. Schwab founded Bethlehem Steel in Bethlehem. Other titans of industry, such as John D. Rockefeller and Jay Gould, also operated in the state. In the latter half of the 19th century, the U.S. oil industry was born in western Pennsylvania, which supplied the vast majority of kerosene for years thereafter. As the Pennsylvania oil rush developed, Pennsylvania's oil boom towns, such as Titusville, rose and fell. Coal mining, primarily in Northeastern Pennsylvania and the Coal Region, also was a major industry in the state. In 1903, Milton S. Hershey began construction on a chocolate factory in Hershey, Pennsylvania; The Hershey Company grew to become the largest chocolate manufacturer in North America. Heinz Company was also founded during this period. These huge companies exercised a large influence on the politics of Pennsylvania; as Henry Demarest Lloyd put it, oil baron John D. Rockefeller "had done everything with the Pennsylvania legislature except refine it". Pennsylvania created a Department of Highways and engaged in a vast program of road-building, while railroads continued to see heavy usage.^{[citation needed]}

The growth of industry eventually provided middle class incomes to working-class households after the development of labor unions helped them gain living wages. However, the rise of unions also led to a rise of union busting with several private police forces springing up. Pennsylvania was the location of the first documented organized strike in North America, and Pennsylvania was the location of two hugely prominent strikes, the Great Railroad Strike of 1877 and the Coal Strike of 1902. The eight-hour day was eventually adopted, and the coal and iron police were banned.

At the beginning of the 20th century, Pennsylvania's economy centered on steel production, logging, coal mining, textile production, and other forms of industrial manufacturing. A surge in immigration to the U.S. during the late 19th and early 20th centuries provided a steady flow of cheap labor for these industries, which often employed children and people who could not speak English from Southern and Eastern Europe. Thousands of Pennsylvanians volunteered during the Spanish–American War. Pennsylvania was an important industrial center in World War I, and the state provided over 300,000 soldiers for the military. On May 31, 1918, the Pittsburgh Agreement was signed in Pittsburgh to declare the formation of the independent state of Czechoslovakia with future Czechoslovak president Tomáš Masaryk.

In 1923, President Calvin Coolidge established the Allegheny National Forest under the authority of the Weeks Act of 1911. The forest is located in the northwest part of the state in Elk, Forest, McKean, and Warren Counties for the purposes of timber production and watershed protection in the Allegheny River basin. The Allegheny is the state's only national forest. Pennsylvania manufactured 6.6 percent of total United States military armaments produced during World War II, ranking sixth among the 48 states. The Philadelphia Naval Shipyard served as an important naval base, and Pennsylvania produced important military leaders, including George C. Marshall, Hap Arnold, Jacob Devers, and Carl Spaatz. During the war, over one million Pennsylvanians served in the armed forces, and more Medals of Honor were awarded to Pennsylvanians than to individuals from any other state.^{[citation needed]}

The Three Mile Island accident was the most significant nuclear accident in U.S. commercial nuclear power plant history. The state was hard-hit by the decline and restructuring of the steel industry and other heavy industries during the late 20th century. With job losses came heavy population losses, especially in the state's largest cities. Pittsburgh lost its place among the top ten most populous cities in the United States by 1950, and Philadelphia dropped to the fifth and later sixth largest city after decades of being among the top three.

After 1990, as information-based industries became more important in the economy, state and local governments put more resources into the old, well-established public library system. Some localities, however, used new state funding to cut local taxes. New ethnic groups, especially Hispanics and Latinos, began entering the state to fill low skill jobs in agriculture and service industries. For example, in Chester County, Mexican immigrants brought the Spanish language, increased Catholicism, high birth rates and cuisine when they were hired to as agricultural laborers; in some rural localities they made up half the population. Meanwhile, Stateside Puerto Ricans built a large community in the state's third largest city, Allentown. They comprised over 40% of the city's population by 2000.

In the 20th century, as Pennsylvania's historical national and even global leadership in mining largely ceased and its steelmaking and other heavy manufacturing sectors slowed, the state sought to grow its service and other industries to replace the jobs and economic productivity lost from the downturn of these industries. Pittsburgh's concentration of universities has enabled it to be a leader in technology and healthcare. Similarly, Philadelphia has a concentration of university expertise. Healthcare, retail, transportation, and tourism are some of the state's growing industries of the postindustrial era. As in the rest of the nation, most residential population growth has occurred in suburban rather than central city areas, although both major cities have had significant revitalization in their downtown areas. Philadelphia anchors the seventh-largest metropolitan area in the country, while Pittsburgh is the center of the twenty-seventh largest metro area in the country. The growth of the Lehigh Valley has made it one of the seventy most populous metro areas in the country, while Pennsylvania also has six other metro areas among the top 200 most populous American metro areas. Philadelphia forms part of the Northeast megalopolis and is associated with the Northeastern United States, while Pittsburgh is part of the Great Lakes megalopolis and is often associated with the Midwestern United States and the Rust Belt.

On September 11, 2001, during the terrorist attacks on the United States, the small town of Shanksville, Pennsylvania received worldwide attention after United Airlines Flight 93 crashed into a field in Stonycreek Township, 1.75 miles (2.82 km) north of the town, killing all 40 civilians and four Al-Qaeda hijackers on board. The hijackers had intended to crash the plane into either the United States Capitol or The White House. After learning from family members via air phone of the earlier attacks on the World Trade Center, however, Flight 93 passengers on board revolted against the hijackers and fought for control of the plane, causing it to crash. It was the only one of the four aircraft hijacked that day that never reached its intended target and the heroism of the passengers has been commemorated.

Beginning in 2003, the Tekko anime convention is held annually in Pittsburgh. In October 2018, the Tree of Life – Or L'Simcha Congregation experienced the Pittsburgh synagogue shooting.

Pennsylvania is 170 miles (274 km) north to south and 283 miles (455 km) east to west. Of a total 46,055 square miles (119,282 km²), 44,817 square miles (116,075 km) are land, 490 square miles (1,269 km²) are inland waters, and 749 square miles (1,940 km) are waters in Lake Erie. It is the 33rd-largest state in the United States. Pennsylvania has 51 miles (82 km) of coastline along Lake Erie and 57 miles (92 km) of shoreline along the Delaware Estuary. Of the original Thirteen Colonies, Pennsylvania is the only state that does not border the Atlantic Ocean.

The boundaries of the state are the Mason–Dixon line (39°43' N) to the south, the Twelve-Mile Circle on the Pennsylvania-Delaware border, the Delaware River to the east, 80°31' W to the west and the 42° N to the north, except for a short segment on the western end, where a triangle extends north to Lake Erie. The state has five geographical regions, namely the Allegheny Plateau, Ridge and Valley, Atlantic Coastal Plain, Piedmont, and the Erie Plain.

Pennsylvania's diverse topography also produces a variety of climates, though the entire state experiences cold winters and humid summers. Straddling two major zones, the majority of the state, except for the southeastern corner, has a humid continental climate (Köppen climate classification Dfb). The southern portion of the state has a humid subtropical climate. The largest city, Philadelphia, has a humid subtropical climate (Köppen Cfa).

Summers are generally hot and humid. Moving toward the mountainous interior of the state, the winter climate becomes colder, the number of cloudy days increases, and snowfall amounts are greater. Western areas of the state, particularly locations near Lake Erie, can receive over 100 inches (250 cm) of snowfall annually, and the entire state receives plentiful precipitation throughout the year. The state may be subject to severe weather from spring through summer into autumn. Tornadoes occur annually in the state, sometimes in large numbers, such as 30 recorded tornadoes in 2011; generally speaking, these tornadoes do not cause significant damage.

Cities include Philadelphia, Reading, Lebanon and Lancaster in the southeast, Pittsburgh in the southwest, and the tri-cities of Allentown, Bethlehem, and Easton in the central east (known as the Lehigh Valley). The northeast includes the former anthracite coal mining cities of Scranton, Wilkes-Barre, Pittston, Nanticoke, and Hazleton. Erie is located in the northwest. State College is located in the central region, Williamsport is in the north-central region with York, Carlisle, and the state capital Harrisburg on the Susquehanna River in the east-central region of the Commonwealth and Altoona and Johnstown in the west-central region.

The state's three most populated cities, in order of size, are Philadelphia, Pittsburgh, and Allentown.

As of the 2020 U.S. census, Pennsylvania had a population of 13,011,844, up from 12,702,379 in 2010. In 2019, net migration to other states resulted in a decrease of 27,718, and immigration from other countries resulted in an increase of 127,007. Net migration to the Commonwealth was 98,289. Migration of native Pennsylvanians resulted in a decrease of 100,000 people. From 2008 to 2012, 5.8% of the population was foreign-born. Pennsylvania is the fifth most populated state in the U.S. after California, Florida, New York, and Texas.

Among Pennsylvania residents, as of 2020, 74.5% were born in Pennsylvania, 18.4% were born in a different U.S. state, 1.5% were born in Puerto Rico, U.S. Island areas, or born abroad to American parent(s), and 5.6% were foreign born. Foreign-born Pennsylvanians are largely from Asia (36.0%), Europe (35.9%), and Latin America (30.6%) with the remainder from Africa (5%), North America (3.1%), and Oceania (0.4%).
The state's largest ancestry groups, expressed as a percentage of total people who responded with a particular ancestry for the 2010 census, are:

Pennsylvania's Hispanic or Latino American population grew by 82.6% between 2000 and 2010, making it one of the largest increases in a state's Hispanic population. The significant growth of the Hispanic or Latino population is due to migration to the state mainly from Puerto Rico, which is a U.S. territory, but to a lesser extent immigration from countries such as the Dominican Republic, Mexico, and various Central and South American nations, as well as from the wave of Hispanic and Latinos leaving New York and New Jersey for safer and more affordable living. The Asian population swelled by almost 60%, which was fueled by Indian, Vietnamese, and Chinese immigration, as well the many Asian transplants moving to Philadelphia from New York. The rapid growth of this community has given Pennsylvania one of the largest Asian populations in the nation by numerical values. The African American population grew by 13%, which was the largest increase in that population amongst the state's peers (New York, New Jersey, Ohio, Illinois, and Michigan). Twelve other states saw decreases in their non-Hispanic white populations. The state has a high in-migration of black and Hispanic people from other nearby states, with eastern and south-central portions of the state seeing the bulk of the increases.

The majority of Hispanic or Latino Americans in Pennsylvania are of Puerto Rican descent, having one of the largest and fastest-growing Puerto Rican populations in the country. Most of the remaining Hispanic or Latino population is made up of Mexicans and Dominicans. Most Hispanic or Latinos are concentrated in Philadelphia, Lehigh Valley and South Central Pennsylvania. Pennsylvania's reported population of Hispanics or Latino Americans, especially among the black race, has markedly increased in recent years. The Hispanic or Latino population is greatest in Bethlehem, Allentown, Reading, Lancaster, York, and around Philadelphia. It is not clear how much of this change reflects a changing population and how much reflects increased willingness to self-identify minority status. As of 2010, it is estimated that about 85% of all Hispanics or Latino Americans in Pennsylvania live within a 150-mile (240 km) radius of Philadelphia, with about 20% living within the city itself.

Among the state's black population, the vast majority in the state are African American. There are also a growing number of blacks of West Indian, recent African, and Hispanic or Latino origins. Most blacks live in the Philadelphia area, Pittsburgh, and South Central Pennsylvania. Non-Hispanic whites make up the majority of Pennsylvania; they are mostly descended from German, Irish, Scottish, Welsh, Italian, and English immigrants. Rural portions of South Central Pennsylvania are famous nationwide for their notable Amish communities. Wyoming Valley, consisting of Scranton and Wilkes-Barre, has the highest percentage of white residents of any metropolitan area (with a population of 500,000 or above) in the U.S., with 96.2% of its population claiming to be white with no Hispanic background. The center of population of Pennsylvania is located in Perry County, in the borough of Duncannon.

As of the 2010 census, Pennsylvania had the fourth-highest proportion of elderly (65+) citizens—15.4%, compared to a national average of 13.0%. According to U.S. Census Bureau estimates, the state's poverty rate was 12.5% in 2017, compared to 13.4% for the United States as a whole.

As of 2010, 90.2% (10,710,239) of Pennsylvania residents age five and older spoke English at home as a primary language, while 4.1% (486,058) spoke Spanish, 0.9% (103,502) German (which includes Pennsylvania Dutch) and 0.5% (56,052) Chinese (which includes Mandarin) of the population over the age of five. In total, 9.9% (1,170,628) of Pennsylvania's population age 5 and older spoke a mother tongue other than English.

Pennsylvania German, spoken by nearly one percent of Pennsylvania's population as of 2010, is often misleadingly called "Pennsylvania Dutch". The term "Dutch" was used to mean "German" (including the Netherlands) before the Latin name for them replaced it (but stuck with the Netherlands). When referring to the language spoken by the Pennsylvania Dutch people (Pennsylvania German), it means German". In fact, Germans, in their own language, call themselves "Deutsch", (Pennsylvania German: "Deitsch"). Pennsylvania Dutch is a descendant of German, in the West Central German dialect family and is closest to Palatine German. Pennsylvania German is still very vigorous as a first language among Old Order Amish and Old Order Mennonites, principally in the Lancaster County and Berks County areas) whereas it is almost extinct as an everyday language outside the plain communities, though a few words have passed into English usage.

Of all the colonies, only Pennsylvania and Rhode Island had the most religious freedom of the original Thirteen Colonies. Voltaire, writing of William Penn in 1733, observed: "The new sovereign also enacted several wise and wholesome laws for his colony, which have remained invariably the same to this day. The chief is, to ill-treat no person on account of religion, and to consider as brethren all those who believe in one God." One result of this uncommon freedom was a wide religious diversity, which continues to the present.

Pennsylvania's population in 2010 was 12,702,379; of these, 6,838,440 (53.8%) were estimated to belong to some sort of organized religion. According to the Association of Religion Data Archives (ARDA) at Pennsylvania State University, the largest religious bodies in Pennsylvania by adherents were the Roman Catholic Church with 3,503,028 adherents, the United Methodist Church with 591,734 members, and the Evangelical Lutheran Church in America with 501,974 members. Since 2014, among the state's religious population, 73% was Christian, according to Pew Research Center. In 2020, the Public Religion Research Institute estimated 68% of the population identified with Christianity. As of 2014, 47% of all Pennsylvanians identified as Protestants, making Protestantism far and away the most prominent religious affiliation among Pennsylvanians. Among all self-identified Christians in the state, however, 24% identified as Catholics, the most of any Christian religious affiliation.

Pennsylvania, especially in the Pittsburgh area and Western Pennsylvania, has one of the largest communities of Presbyterians in the nation, being the third highest by percentage of population and the largest outright in membership as Protestant Christians. The Presbyterian Church (USA), with about 250,000 members and 1,011 congregations, is the largest Presbyterian denomination while the Presbyterian Church in America is also significant, with 112 congregations and approximately 23,000 adherents; the EPC has around 50 congregations, as well as the ECO according to 2010 estimates. The fourth-largest Protestant denomination, the United Church of Christ, has 180,000 members and 627 congregations in the state. The American Baptist Churches USA (also referred to as the Northern Baptist Convention) is based in King of Prussia, Pennsylvania.

Pennsylvania was the center state of the German Reformed denomination from the 1700s. Bethlehem, Pennsylvania is one of the headquarters of the Moravian Church in the U.S. Pennsylvania also has a very large Amish population, second only to Ohio among U.S. states. As of 2000, there was a total Amish population of 47,860 in Pennsylvania and an additional 146,416 Mennonites and 91,200 Brethren. The total Anabapist population including Bruderhof was 232,631, about two percent of the population. While Pennsylvania owes its existence to Quakers, and much of the historic character of the Commonwealth is ideologically rooted in the teachings of the Religious Society of Friends (as they are officially known), practicing Quakers are a small minority of about 10,000 adherents as of 2010.