Pittsburgh is a city in the Commonwealth of Pennsylvania and the county seat of Allegheny County. It is the second-most populous city in Pennsylvania after Philadelphia and the 68th-most populous city in the U.S. with a population of 302,971 as of the 2020 census. The city anchors the Pittsburgh metropolitan area of Western Pennsylvania. Its population of 2.457 million is the largest in both the Ohio Valley and Appalachia, the second-largest in Pennsylvania, and the 26th-largest in the U.S. Pittsburgh is the principal city of the greater Pittsburgh–Weirton–Steubenville combined statistical area that extends into two neighboring states, Ohio and West Virginia.