Chester County, colloquially known as Chesco, is a county in the U.S. state of Pennsylvania. The county seat is West Chester. Chester County was one of the three original Pennsylvania counties created by William Penn in 1682. It was named for Chester, England. Chester County is part of the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD Metropolitan Statistical Area. Eastern Chester County is home to many communities that comprise part of the Main Line western suburbs outside of Philadelphia, while part of its southernmost portion is considered suburban Wilmington, along with southwest Delaware County.