Philadelphia County is the most populous of the 67 counties of Pennsylvania and the 24th-most populous county in the nation. As of the 2020 census, the county had a population of 1,603,797. It is coextensive with Philadelphia, the nation's sixth-largest city. The county is part of the Southeast Pennsylvania region of the state. Philadelphia County is one of the three original counties, along with Chester and Bucks counties, founded by William Penn in November 1682.