^Westbound trailblazer leaving Interstate 255 near Centreville, February 2023.
Illinois Route 15 runs east-west across the entire width of southern Illinois, from East Saint Louis through Mount Vernon to Mount Carmel on the Wabash River. This closely parallels the Interstate 64corridor.
The western end of Illinois 15 is in East Saint Louis, near the combination of Interstates 55 and 64...
At Alorton, Illinois 15 meets the northern end of Illinois 163: