| State: | IL |
| Type: | IL |
| Maint: | IDOT |
| Route: | 138 |
| Map Custom: | yes |
| Map Notes: | IL 138 highlighted in red |
| Length Mi: | 14.95 |
| Length Round: | 2 |
| Length Ref: | [1] |
| Direction A: | West |
| Terminus A: | in Bunker Hill |
| Junction: | in White City |
| Direction B: | East |
| Terminus B: | Illinois Street in Mount Olive |
| Counties: | Macoupin |
| Established: | 1942[2] |
| Previous Route: | 137 |
| Previous Type: | IL |
| Next Type: | IL |
| Next Route: | 140 |
Illinois Route 138 is a state highway in southwestern Illinois. It runs from Illinois Route 159 north of Bunker Hill to the city of Mount Olive at Illinois Street, a former alignment of U.S. Route 66. This is a distance of 14.95miles.
Illinois 138 runs east - west, with a bend north through the city of Benld. It is a two-lane surface road for its entire length. South of Benld, it also overlaps Illinois Route 4 for a few miles.
SBI Route 138 ran from Mount Carmel to Grayville; in 1937, this became Illinois Route 1. It was put on its current alignment in 1942, replacing parts of Illinois Route 38.[2]