Eastport is a city and archipelago in Washington County, Maine, United States. The population was 1,288 at the 2020 census, making Eastp…Eastport is a city and archipelago in Washington County, Maine, United States. The population was 1,288 at the 2020 census, making Eastport the least-populous city in Maine. The principal island is Moose Island, which is connected to the mainland by a causeway. Eastport is the easternmost city in the continental United States.