Pennsylvania ( (listen) PEN-səl-VAY-nee-ə; Pennsylvania German: Pennsilfaani), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, and Appalachian regions of the United States. It borders Delaware to the southeast, Maryland to the south, West Virginia to the southwest, Ohio to the west, Lake Erie and the Canadian province of Ontario to the northwest, New York to the north, and the Delaware River and New Jersey to the east.
Pennsylvania is the fifth-most populous state in the nation with over 13 million residents as of 2020. It is the 33rd-largest state by area and ranks ninth among all states in population density. Nearly half the population, over 6.2 million people as of 2020, is concentrated in the southeastern Delaware Valley metropolitan area, centered around Philadelphia, the state's largest and nation's sixth most populous city. One third of the state's residents live in Greater Pittsburgh (2.37 million) in the southwest, centered around Pittsburgh, the state's second-largest city and the largest in Western Pennsylvania. The subsequent five most populous cities are Allentown, Erie, Reading, Bethlehem, and Scranton. The state capital is Harrisburg.
Pennsylvania's geography is highly diverse: the Appalachian Mountains run through its center, while the Allegheny and Pocono Mountains span much of the northeast; close to 60% of the state is forested. While it has only 140 miles (225 km) of waterfront along Lake Erie and the Delaware River, Pennsylvania has more navigable rivers than any other state, including the Delaware, Ohio, and Pine Creek.
Pennsylvania was founded in 1681 through royal land grant to William Penn, son of the state's namesake; the southeast portion was once part of the colony of New Sweden. Established as a haven for religious and political tolerance, the Province of Pennsylvania was noteworthy for its relatively peaceful relations with native tribes, innovative government system, and religious pluralism. Pennsylvania was one of the thirteen British colonies from which the nation ultimately was formed.
Pennsylvania played a vital and historic role in the quest for independence. Its largest city, Philadelphia, was the gathering place of the nation's founding fathers and home to much of the thinking, activism, and writing that inspired the American Revolution. Philadelphia hosted the First Continental Congress in Carpenters' Hall in 1774, and, beginning the following year, the Second Continental Congress in Independence Hall, which unanimously adopted the Declaration of Independence, a document that historian Joseph Ellis has described as "the most potent and consequential words in American history" and which formally launched the American Revolutionary War.
In Philadelphia, the Second Continental Congress, on June 21, 1778, ratified the Articles of Confederation, which served as the foundation for the ultimate development and ratification of the U.S. Constitution; Pennsylvania became the second state (after Delaware, which had previously been part of Pennsylvania as the three lower counties) to ratify the Constitution on December 12, 1787. On eight separate occasions prior to the construction of Washington, D.C. as the nation's capital, a Pennsylvania city served as the nation's capital (Philadelphia from 1775 to 1776, 1777, twice in 1778, 1781, and 1790; York in 1777; and Lancaster in 1777).
During the American Civil War, Pennsylvania's 360,000 Union Army volunteers proved influential in strengthening the Union, successfully guarding the national capital of Washington, D.C. following the fall of Fort Sumter, and later leading daring raids against Confederate Army strongholds in the Deep South. The bloodiest battle of the Civil War with over 50,000 casualties, and one of the Union Army's most important victories, was fought on Pennsylvania soil at Gettysburg over three days in July 1863. Lincoln's 271-word address dedicating Gettysburg National Cemetery on November 19, 1863 remains one of the best known speeches in American history
In the late 19th and 20th centuries, Pittsburgh-based U.S. Steel, Bethlehem-based Bethlehem Steel, and other Pennsylvania manufacturing companies inspired the Industrial Revolution and contributed to the development of much of the nation's early infrastructure, including key bridges, skyscrapers, and warships, tanks, and other military hardware that proved vital to U.S.-led victories in World War I, World War II, and the Cold War. Since Pennsylvania's 1787 founding, a number of influential Pennsylvanians have contributed significantly to the nation in many fields, including the military, politics, business, scientific innovation, thought leadership, philanthropy, music, art, and sports.