West Chester is a borough and the county seat of Chester County, Pennsylvania. Located within the Philadelphia metropolitan area, the borough had a population of 18,461 at the 2010 census. West Chester is the mailing address for most of its neighboring townships. When calculated by mailing address, the population as of the 2010 U.S. Census was 108,696, which would make it the 10th largest city by mailing address in the state of Pennsylvania.