Barnstable County is a county in the U.S. state of Massachusetts. At the 2020 census, the population was 228,996. The county seat is Barnstable. The county consists of Cape Cod and associated islands. Barnstable County was formed as part of the Plymouth Colony on June 2, 1685, including the towns of Falmouth, Sandwich, and others to the east and north on Cape Cod. Plymouth Colony was merged into the Province of Massachusetts Bay in 1691.