Delaware County, Pennsylvania

Delaware County
County
Delaware County Courthouse in Media, Pennsylvania
Location within the U.S. state of Pennsylvania
Pennsylvania's location within the U.S.
Coordinates: 39°55′N 75°24′W / 39.92°N 75.40°W / 39.92; -75.40
Country United States
State Pennsylvania
FoundedSeptember 26, 1789
Named afterDelaware River
SeatMedia
Largest TownshipUpper Darby
Other citiesChester
Area
  Total
191 sq mi (490 km2)
  Land184 sq mi (480 km2)
  Water6.8 sq mi (18 km2)  3.5%
Population
 (2020)
  Total
576,830
  Estimate 
(2023)
576,720
  Density3,000/sq mi (1,200/km2)
Congressional district5th
Websitedelcopa.gov
DesignatedOctober 3, 1982

Delaware County, colloquially referred to as Delco, is a county 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 Southeast 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 PhiladelphiaCamdenWilmington, PA–NJDEMD metropolitan statistical area. Its county seat is Media.