Bucks County is a county located in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 628,270; it is the fourth-most populous county in Pennsylvania. The county seat is Doylestown. The county is named after the English county of Buckinghamshire or more precisely, its abbreviation. Bucks County constitutes part of the northern boundary of the Philadelphia–Camden–Wilmington, PA–NJ–DE–MD Metropolitan Statistical Area, more commonly known as the Delaware Valley.