The East Branch Sebasticook River is a tributary of the Sebasticook River in central Maine in the United States. It is part of the Kennebec River watershed. From the outflow of Lake Wassookeag in Dexter, the river runs about 12.7 miles (20.4 km) south to Sebasticook Lake. From the outflow of the lake in Newport, the river runs about 9.5 miles (15.3 km) southwest to its confluence with the Sebasticook in Detroit.