Pennsylvania, officially the Commonwealth of Pennsylvania, is a state located in the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Maryland to its south, forming the Mason-Dixon Line, West Virginia to its southwest, Ohio to its west, the Canadian province of Ontario to its northwest via Lake Erie, New York to its north, and the Delaware River and New Jersey to its east. Pennsylvania's most populous city is Philadelphia, and the state capital is Harrisburg. Among all US states, Pennsylvania is the fifth-most populous with over 13 million residents as of the 2020 United States census, the ninth-highest by population density, and the 33rd-largest by land area. The largest metropolitan statistical area is the Philadelphia metropolitan area in southeastern Pennsylvania, also known as the Delaware Valley and centered on Philadelphia, the sixth-most populous U.S. city. Pennsylvania's second-largest metropolitan area, Greater Pittsburgh, is centered in and around Pittsburgh, the commonwealth's second-largest city.