Philadelphia County is a
county located in the
commonwealth of
Pennsylvania. At the
2010 census, the population was 1,526,006, making it the most populous county in the state, despite being the second smallest county in the state by land area. Philadelphia County is one of the three original counties, along with
Chester and
Bucks counties, created by
William Penn in November 1682. Since 1854, the county has been coterminous with the city of
Philadelphia, which also serves as its
seat. It is the most populous county in the United States coterminous with a municipality.