Pennsylvania ( PEN-səl-VAY-nee-ə) (Pennsylvania German: Pennsilfaani), officially the Commonwealth of Pennsylvania, is a state in the Northeastern, Great Lakes, Appalachian, and Mid-Atlantic regions of the United States. The Commonwealth is bordered by 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 New Jersey to the east, while the Appalachian Mountains run through its middle.

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 13th-largest city is Harrisburg. Pennsylvania has 140 miles (225 km) of waterfront along Lake Erie and the Delaware River.

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 Philadelphia, the state’s largest city. 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.