The Farmington River is a river, 46.7 miles (75.2 km) in length along its main stem, located in northwest Connecticut with major tributaries extending into southwest Massachusetts. The longest route of the river, from the origin of its West Branch, is 80.4 miles (129.4 km) long, making it the Connecticut River's longest tributary by 2.3 miles (3.7 km) over the major river directly to its north, the Westfield River. The Farmington River's watershed covers 609 square miles (1,580 km2). Historically, the river played an important role in small-scale manufacturing in towns along its course, but it is now mainly used for recreation and drinking water.

The Connecticut River is the longest river in the New England region of the United States, flowing roughly southward for 406 miles (653 km) through four states. It rises 300 yards south of the U.S. border with Quebec, Canada, and discharges at Long Island Sound. Its watershed encompasses 11,260 square miles (29,200 km2), covering parts of five U.S. states and one Canadian province, via 148 tributaries, 38 of which are major rivers. It produces 70% of Long Island Sound's fresh water, discharging at 18,400 cubic feet (520 m3) per second.