Housatonic, river, rising in the Berkshire Hills, northwestern Massachusetts. It flows generally south through Massachusetts and Connecticut before emptying into Long Island Sound between Devon and Stratford, Connecticut. The total course of the river, noted for its scenic beauty, is 238 km (148 mi). It has been an important source of waterpower since colonial times, when mill towns such as Dalton and Pittsfield, Massachusetts, were established along it.