There are 6 US Post Offices in Dukes County serving a total of 16,512 residents equating to 2,752 residents per post office. It's estimated that approximately 26,355 packages are handled across the 6 county post offices annually. Dukes County is a county located in the U.S. state of Massachusetts. As of the 2010 census, the population was 16,535, 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 the island of Martha's Vineyard (including Chappaquiddick Island), the Elizabeth Islands (including Cuttyhunk), the island of Nomans Land, and other associated islets."