| State: | IL |
| Type: | IL |
| Maint: | IDOT |
| Route: | 155 |
| Map Custom: | yes |
| Map Notes: | IL 155 highlighted in red |
| Length Mi: | 10.81 |
| Length Round: | 2 |
| Length Ref: | [1] |
| Direction B: | East |
| Direction A: | West |
| Terminus A: | Fort de Chartres State Historical Site in Prairie du Rocher |
| Terminus B: | in Ruma |
| Counties: | Randolph |
| Established: | 1924[2] |
| Previous Route: | 155 |
| Previous Type: | I |
| Next Route: | 156 |
| Next Type: | IL |
Illinois Route 155 is an east - west state highway in southwestern Illinois. It runs from Fort de Chartres – outside of Prairie du Rocher – to Illinois Route 3 in Ruma. This is a distance of approximately 10.81miles.
Illinois 155 serves as a spur from Illinois Route 3 through Prairie du Rocher and on to Fort de Chartres. It is recognized as a spur of the Great River Road. It is also part of the Lincoln Heritage Trail.[3] Illinois 155 is a two-lane road from Fort de Chartres all the way to Illinois 3.
Illinois Route 155 was established in 1924 with the second batch of SBI routes. Its route has not changed since 1924.