Delaware County was created on September 26, 1789, from part of Chester County and named for the Delaware River.
Its county seat, since 1851, has been Media. As of 2010, the population was 558,979, making it Pennsylvania's fifth most populous county. The county, immediately adjacent to and west of Philadelphia, is part of the Delaware Valley area. Delaware County is the only county covered in its entirety by area code 610. 2,600 acres of the county are occupied by the Ridley Creek State Park.
Map of Delaware County