Illinois Route 394 is a four-lane state freeway that travels south from Thornton at the Interstate 294/Interstate 94/Interstate 80 (Tri-State Tollway/Bishop Ford Freeway; this route is an extension of the latter freeway) interchange to Illinois Route 1 south of Steger and Crete. Before taking the Illinois 394 route, it was known as Illinois 1. Illinois 394 is 14.63 miles (23.54 km) long.

Although not an Interstate highway, Illinois 394 is an Interstate standard highway until its junction with U.S. Highway 30 (Lincoln Highway) near Chicago Heights.

In 2006 and 2007, Illinois 394 was reconstructed north of Glenwood–Dyer Road as part of the massive Kingery Expressway reconstruction effort. The intersection with Interstates 80, 94 and 294 was improved in the following areas: