The Thames River is a short river and tidal estuary in the state of Connecticut. It flows south for 15 miles (24 km) through eastern Connecticut from the junction of the Yantic River and Shetucket River at Norwich, Connecticut, to New London and Groton, Connecticut, which flank its mouth at Long Island Sound. The Thames River watershed includes a number of smaller basins and the 80-mile (130 km) long Quinebaug River, which rises in southern Massachusetts and joins the Shetucket River about four miles northeast of Norwich.

Connecticut is the southernmost state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capital is Hartford, and its most populous city is Bridgeport. Connecticut lies between the major hubs of New York City and Boston along the Northeast Corridor, where the New York metropolitan area, which includes six of Connecticut's seven largest cities, extends well into the southwestern part of the state. Connecticut is the third-smallest state by area after Rhode Island and Delaware, and the 29th most populous with slightly more than 3.6 million residents as of 2020, ranking it fourth among the most densely populated U.S. states.