Mattapoisett sits on the shores of Buzzards Bay with Fairhaven to the west, Marion to the east, and Acushnet and Rochester to the north.

The town of Mattapoisett covers 18 square miles, all of which is located within the Buzzards Bay watershed. As of the 2010 Census, Mattapoisett was home to 6,045 residents. Its coastline extends 26 miles along Nasketucket Bay, Mattapoisett Harbor, Aucoot Cove, and the Mattapoisett River.