Tonty Canyon is "temporarily closed" right now due to water eroding the trail. This closure has been long lasting and there is no immediate plan for the trail to be improved. Normally Tonty Canyon would be accessible from two different paths. The first access point is directly from Lasalle Canyon and the second access point is from the River Trail. Here is a quote from the Illinois Department of Natural Resources website regarding trail safety and navigation:
The trails are open all year, but hikers are urged to exercise extreme caution and to stay on official trails. To keep you oriented, trail maps are located at all trail access points, intersections and points of interest. There are colored posts along the trails, corresponding to colors on the maps, and letter symbols on the trail brochure to further assist you. Finally, yellow dots on posts indicate that you are moving away from the lodge or visitor center, and white dots mean you are returning.