The Tomahawk River is a river in the U.S. state of Wisconsin.It is the largest tributary of the Wisconsin River in terms of flow. It begins at Tomahawk Lake in southern Vilas County, flows through Oneida County, and terminates at Lake Mohawksin in Tomahawk. It flows through the Willow Reservoir and Lake Nokomis (artificial reservoirs), and Kawaguesaga Lake and Minocqua Lake (natural lakes).At one time the Tomahawk River was known as the Little Wisconsin River.