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 longest tributary by 2.3 miles (3.7 km) over the Westfield River directly to its north.
The headwaters of the Farmington River consist of the East and West Branches.
The West Branch begins at the outlet of Hayden Pond in Otis, Massachusetts, while the East Branch begins in Hartland, Connecticut, at the confluence of Pond, Hubbard and Valley Brooks.
The East Branch has been impounded along the first 11 miles of its course by the Saville Dam to create the Barkhamsted Reservoir and Lake McDonough, exiting the latter in New Hartford, Connecticut, and joining the West Branch one mile south of the lake. Upper reaches of the river generally flow southward, but the river turns northward in Farmington, Connecticut, and runs mostly north and east until it flows into the Connecticut River in Windsor, Connecticut.
