Illinois State Route 203 runs briefly in Northwestern St. Clair County. It runs from I-55/70/U.S. Rt. 40 to the St. Clair/Madison County Line. IL St Rt 203 intersects the following highways in St. Clair County. Madison
IL St Rt 203 is not multi-plexed in St. Clair County. IL St Rt 203 intersects the following highways in St. Clair County. Interstate 55, at Madison. Interstate 70, at Madison.
NB IL St Rt 203 near Gateway Speedway. A BGS on NB I-55; EB I-70/U.S. Rt. 40. NB IL St Rt 203 at the southern start. The southern end point. (September, 2007) The southern end marker. The "0" St. Clair County mile marker.
