The Sudbury River is a 52.6 km tributary of the Concord River in Middlesex County, Massachusetts, in the United States.
Originating in the Cedar Swamp in Westborough, Massachusetts, near the boundary with Hopkinton, the Sudbury River meanders generally northeast, through Fairhaven Bay, and to its confluence with the Assabet River at Egg Rock in Concord, Massachusetts, to form the Concord River. It has a 420 km2 drainage area.
