Edgartown is a town located on Martha's Vineyard in Dukes County, Massachusetts, United States. It is the county seat of Dukes County. Edgartown has the largest population and area in the entire Dukes County and Martha's Vineyard. In 1642. Rev. Thomas Mayhew, Jr. led a group of families to start a colony on the island after its purchase by his father Thomas Mayhew. Originally called Great Harbor, it was incorporated in 1671, and is one of the two original towns on Martha's Vineyard, along with Tisbury. The town's current name is in honor of Edgar, the young son of James II of England who died at the age of three in 1671. The younger Mayhew began his work which led to his becoming the first church planting Protestant missionary after he settled in Edgartown. A Wampanoag Indian named Hiacoomes who lived nearby became his partner in founding the churches in the Indian communities.