Marion is tucked between Mattapoisett to the west, Wareham to the east, and Rochester to the north. The entire town is located within the Buzzards Bay watershed.

At 4,907 residents as of the 2010 Census, the town of Marion has one of the smallest populations of any town on Buzzards Bay. Marion’s land area covers 14 square miles, all of which is located within the Buzzards Bay watershed.