The Mackinaw River, also called Mackinac River, is a 130-mile-long (210 km) river in the U.S. state of Illinois. It flows through what was once the Grande Prairie region of central Illinois. This region is now a zone of intensive crop farming, and high-productivity farming techniques have extensively altered the river from its natural state.
The headwaters of the river are located near Sibley, Illinois, in western Ford County. Flowing west through McLean County, the Mackinaw River provides drainage to part of the Bloomington-Normal metropolitan area.
The Mackinaw River then flows west through Woodford County before turning southwest and draining much of Tazewell County. The river's course describes several bends and meanders typical of alluvial rivers before flowing northwards into the Illinois River just south of Pekin.
A 1,448-acre (586 ha) parcel of Mackinaw River hillside land, in far eastern Tazewell County just east of Mackinaw, is preserved as the Mackinaw River State Fish and Wildlife Area, a state game preserve.
Most central Illinois towns and cities were founded as a result of transportation on local railroads, not rivers. Even though this river drains much of three counties, only one town of any size, Mackinaw, is actually located on the Mackinaw River.
It is believed that the Mackinaw River was named in the early 19th century in honor of an unnamed fur trader from Mackinac Island, Michigan who traded goods at or near the river.