It runs from Fort de Chartres – outside of Prairie du Rocher – to Illinois Route 3 in Ruma.

This is a distance of approximately 10.81 miles (17.40 km).

[1] 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.

The entire route is in Randolph County.