Philadelphia County is a county located in the U.S. State of Pennsylvania. It is coterminous with the city of Philadelphia which also serves as its seat. In 2008, the United States Census Bureau estimated the population had grown to 1,540,351, making it the most populous county in the state. Philadelphia County is one of the three original counties, along with Chester and Bucks counties, created by William Penn in November 1682.
This county is part of the Delaware Valley area and is one of the flagships of the Greater Philadelphia MSA.