Chester County is a county located in the U.S. state of Pennsylvania. As of 2000, the population was 433,501. The county seat is West Chester. It is the highest-income county measured per capita and by median household income in Pennsylvania, and has the 21st highest gross adjusted income in the nation (as of 2009).
Chester County is one of the three original counties of Pennsylvania created by William Penn in 1682. It is named for Cheshire, England. It is part of the Delaware Valley area, and is the only Delaware Valley county in Pennsylvania that does not border Philadelphia, though it is close.