Delaware

Delaware County colloquially referred to as Delco is a county located in the U.S. state of Pennsylvania that borders Philadelphia. With a population of 566,747, 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.

Its county seat is Media. Until 1850, Chester was the county seat of Delaware County and, before that, of Chester County.