Delaware County, Pennsylvania

Not to be confused with Delaware Valley, which is the entire Philadelphia metropolitan area.

Delaware County, Pennsylvania
County
Delaware County Courthouse in Media, Pennsylvania
Flag Seal
Location within the U.S. state of Pennsylvania
Interactive map of Delaware County, Pennsylvania
Coordinates: 39.92°N 75.40°W / 39.92; -75.40
Country	United States
State	Pennsylvania
Founded	September 26, 1789
Named for	Delaware River
Seat	Media
Largest Township	Upper Darby
Other cities	Chester
Area
• Total	191 sq mi (490 km2)
• Land	184 sq mi (480 km2)
• Water	6.8 sq mi (18 km2)  3.5%
Population  (2020)
• Total	576,830
• Estimate  (2025)	580,937
• Density	3,130/sq mi (1,210/km2)
Congressional district	5th
Website	delcopa.gov
Pennsylvania Historical Marker
Designated	October 3, 1982

Delaware County, colloquially referred to as Delco, is in the Commonwealth of Pennsylvania. With a population of 576,830 as of the 2020 census, it is the fifth-most populous county in Pennsylvania and the third-smallest in area. The county was created on September 26, 1789, from part of Chester County and named for the Delaware River. The county is part of the Philadelphia metropolitan area region of the commonwealth.

Delaware County borders Philadelphia, the nation's sixth-most populous city, to its northeast. It also is adjacent to the city-county of Philadelphia County and is included in the Philadelphia–Camden–Wilmington, PA–NJ–DE–MD metropolitan statistical area. Its county seat is Media, which is located near the center of the county.