Chester, Philadelphia, and Bucks Counties were the three original Pennsylvania counties created by William Penn in 1682. At that time Chester County's borders were Philadelphia County to the north, the Susquehanna River to the west, the Delaware River to the east, and Delaware and Maryland to the south.

The fourth county in the state, Lancaster County, was formed from Chester County on May 10, 1729. On March 11, 1752 Berks County was formed from the northern section of Chester County, as well as parts of Lancaster and Philadelphia Counties.

The original Chester County seat was the naval shipbuilding city of Chester. However, it became part of Delaware County when it was formed from the eastern portion of the Chester County on September 26, 1789. This took the county seat out of Chester County, so West Chester became the new county seat that year, and has remained so to the present.

It was named for Cheshire, England. It is part of the Delaware Valley area.

"Chester County, Pennsylvania." Wikipedia, The Free Encyclopedia. 16 Apr 2007, 01:09 UTC. Wikimedia Foundation, Inc. 28 Apr 2007 url.

Chester County was founded in 1682 as one of the original counties in Pennsylvania. Counties formed from Chester include Delaware, Lancaster.

Bonsall, Charlesworth, Eaton, Elliott, Evans, Haines, Hood, Humphrey, Kirk, Matlack, Stout