Illinois Route 116 (abbreviated IL 116) is a cross-state rural state highway that runs from U.S. Route 34 by Gladstone east to the intersection of U.S. Route 45 (North Front Street) and Old U.S. Route 45, on the north side of Ashkum. This is a distance of 176.07 miles (283.36 km).

The western terminus of Illinois 116 is approximately ten miles (16 km) from the Iowa state line, east of Burlington, Iowa. It crosses the Illinois River from Peoria to East Peoria with Illinois Route 8 and Illinois Route 29 on the Cedar Street Bridge.

On the southeast side of the Illinois River, it and U.S. Route 150 form a wrong-way concurrency. Travelling geographic northeast along the river, U.S. 150 is marked west before crossing the river to enter Peoria, and Illinois 116 is marked east. Travelling geographic southwest, U.S. 150 is marked east before branching to Morton, and Illinois 116 is marked west before crossing the river to enter Peoria on its southern side.

U.S. Route 124 (abbreviated US 124) was a U.S. Highway that was commissioned from 1926 to 1938, and was located in Illinois, running from Peoria through Biggsville. It was approximately 80 miles (130 km) in length, and followed much of the route of IL 116 prior to its decommissioning. SBI Route 116 originally ran separately from east of Ashkum to East Peoria.

US 124 was one of the original 1928 US routes in IL (since US routes didn't appear on IL maps until then). It originally went from Peoria to Galesburg, along with the then IL-8, via Farmington and Maquon on the route of the current IL 116 west from Peoria to IL-97, north to IL-8, west to IL-97, then northwest on IL-97 to Galesburg, with the last few miles on the current US 150.

In 1934, US 124 was rerouted west on the current IL 116 to near Biggsville, where it connected to US 34 (for access to Mississippi River crossing into Iowa). West bound traffic from Peoria had a choice. Proceed along US 24 to cross the Mississippi River at Quincy (south-west route) - the old Peoria to Quincy stage coach route, or take US 124 to cross the Mississippi River (US 34) at Burlington, IA (north-west route).

With the completion of Interstate 474 as a western bypass of Peoria in 1978, an Interstate connector (Exit 3 on Interstate 474) was constructed as the eastern terminus for the proposed western Illinois expressway (Peoria to Kansas City via Macomb and Quincy). The connector provides access to IL 116.

Illinois Route 97A was a short rural spur (state maintained) that ran from U.S. Route 124 (now IL 116) south of Media south to the community of Raritan, Illinois.