^Eastbound trailblazer with Illinois 158 joining along, as both routes depart from Illinois 13 on the east side of Belleville, February 2023.
Illinois Route 177 runs east-west, roughly along the Interstate 64 corridor, in southwestern Illinois. It begins in Belleville and runs easterly to end at US Route 51 in Irvington, south of Centralia.
The western beginning of Illinois 177 is situated in Belleville, where Illinois 13 departs and turns southerly off of Illinois 158. Illinois 158 accompanies Illinois 177 as it leaves Belleville going east:
Illinois 158 departs Illinois 177, turning northerly, west of Mascoutah...