MIDDLE RIVER, Stafford. Intermittent sections from Edson Brook to Willimantic River.The Willimantic River is a tributary of the Shetucket River, approximately 25 mi (40 km) long in northeastern Connecticut in the New England region of the United States. It is formed in northern Tolland County, near Stafford Springs by the confluence of Middle River and Furnace Brook. It flows south to the city of Willimantic, where it joins the Natchaug River to form the Shetucket.