The Five Mile River is a 23.5-mile-long (37.8 km) river located in Connecticut's northeast corner which flows through the towns of Thompson, Putnam, and Killingly.

The Assawaga received its English name from the fact that the first land laid out upon it was "supposed to be about five miles from" Woodstock, Connecticut.

The Five Mile River has several dams, most of which are remnants of defunct mills and some of which are still used by local industry.

Its largest impoundment is Quaddick Reservoir.

The best examples of surviving mill villages are Killingly in villages such as Pineville, Ballouville, Attawaugan, and Dayville.