Delaware County, colloquially referred to as Delco, is a county located in the U.S. state of Pennsylvania. With a 2013 census population of 561,973, 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. Socioeconomically, Delaware County consists of mostly working class, middle-class and upper middle class communities. Delaware County is the only county covered in its entirety by area codes 610 and 484
Delaware County lies in the river and bay drainage area named "Delaware" in honor of Thomas West, 3rd Baron De La Warr, Governor of the nearby English colony of Virginia. The land was "discovered" and explored by Henry Hudson in 1609, and over the next several decades it was variously claimed and settled by the Swedes, the Dutch, and the English. Its original human inhabitants were the Lenni-Lenape tribe of American Indians.
Once the Dutch were defeated and the extent of New York was determined, King Charles II of England made his grant to William Penn in order to found the colony which came to be named Pennsylvania. Penn divided his colony into three counties: Bucks, Philadelphia, and Chester. The riverfront land south of Philadelphia, being the most accessible, was quickly granted and settled. In 1789, the eastern portion of Chester County was divided from the rest. Despite that the eastern portion was the first settled and contained the town of Chester, it was named Delaware County for its river.
Curtesy of Wikipedia