There are 44 US Post Offices in Delaware County serving a total of 648,846 residents equating to 14,747 residents per post office. It's estimated that approximately 1,035,631 packages are handled across the 44 county post offices annually. Delaware County, colloquially referred to as Delco, is a county located in the U.S. state of Pennsylvania. With a 2010 census population of 558,979, it is the fifth most populous county in Pennsylvania, and the third most compact. Its county seat is Media. The county was created on September 26, 1789, from part of Chester County and named for the Delaware River. Chester City, prior to 1851, was the county seat of both Delaware County and, before that, of Chester County. Delaware County is adjacent to the city-county of Philadelphia and is included in the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD Metropolitan Statistical Area. Delaware County is the only county covered in its entirety by area codes 610 and 484."