Illinois Route 128 is a north–south state road in east-central Illinois. It runs from Interstate 70 in Altamont to Illinois Route 121 in Dalton City. This is a distance of 55.57 miles (89.43 km).

Illinois 128 is a two-lane, rural surface road for its entire length. Immediately north of Interstate 70, it overlaps U.S. Route 40 for 3 miles (5 km). It is also concurrent with Illinois Route 16 near Shelbyville.

Illinois 128 may or may not run through Moultrie County, depending on its exact routing, as the route appears to run along portions of the Shelby/Moultrie and Macon/Moultrie county lines.

SBI Route 128 originally ran from U.S. Route 40 (originally Illinois Route 11) to Illinois 16 west of Shelbyville. In 1937, it replaced Illinois Route 169 north of Shelbyville to Dalton City. Finally, as Interstate 70 was being built in the 1950s and 1960s, it was extended along U.S. 40 to Altamont.