Cape Cod Bay is a large bay of the Atlantic Ocean adjacent to the U.S. state of Massachusetts.
Measuring 604 square miles (1,560 km2) below a line drawn from Brant Rock in Marshfield to Race Point in Provincetown, Massachusetts, it is enclosed by Cape Cod to the south and east, and Plymouth County, Massachusetts, to the west.
To the north of Cape Cod Bay lie Massachusetts Bay and the Atlantic Ocean. Cape Cod Bay is the southernmost extremity of the Gulf of Maine.
Cape Cod Bay is one of the bays adjacent to Massachusetts that give it the name Bay State. The others are Narragansett Bay, Buzzards Bay, and Massachusetts Bay.
