Pennsylvania, officially the Commonwealth of Pennsylvania, is a state located in the northeastern and Mid-Atlantic regions of the United States. The Appalachian Mountains run through its middle. The Commonwealth 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 New Jersey to the east.Pennsylvania is the 33rd-largest, the 6th-most populous, and the 9th-most densely populated of the 50 United States. The state's five most populous cities are Philadelphia, Pittsburgh, Allentown, Erie, and Reading . The state capital, and its ninth-largest city, is Harrisburg. Pennsylvania has 140mi of shoreline along Lake Erie and the Delaware Estuary.