Dukes County is a county in the U.S. state of Massachusetts. At the 2020 census, the population was 20,600, making it the second-least populous county in Massachusetts. Its county seat is Edgartown. Dukes County comprises the Vineyard Haven, MA Micropolitan Statistical Area. The county consists of 32 named islands, the largest of which is Martha's Vineyard. It also includes Chappaquiddick Island, the Elizabeth Islands, including Cuttyhunk, and Nomans Land.