Pennsylvania is the 33rd-largest state by area, and the 5th-most populous state according to the most recent official U.S. Census count in 2010. It is the 9th-most densely populated of the 50 states. Pennsylvania's two most populous cities are Philadelphia (1,580,863), and Pittsburgh (302,407). The state capital and its 10th largest city is Harrisburg. Pennsylvania has 140 miles (225 km) of waterfront along Lake Erie and the Delaware Estuary.

The state is one of the 13 original founding states of the United States; it came into being in 1681 as a result of a royal land grant to William Penn, the son of the state's namesake. Part of Pennsylvania (along the Delaware River), together with the present State of Delaware, had earlier been organized as the Colony of New Sweden. It was the second state to ratify the United States Constitution, on December 12, 1787. Independence Hall, where the United States Declaration of Independence and United States Constitution were drafted, is located in the state's largest city of Philadelphia. During the American Civil War, the Battle of Gettysburg was fought in the south central region of the state. Valley Forge near Philadelphia was General Washington's headquarters during the bitter winter of 1777–78.