^Illinois Route 37 getting its start near Cairo at US Route 51, February 2023.
Illinois Route 37 connects Effingham with Cairo, running through places like Marion in the backbone of southernmost Illinois. It parallels Interstate 57 for its entire length; south of Effingham, Interstate 57 switches from following US Route 45 to following Illinois 37 through the rest of Southern Illinois. It runs north-south overall, with a bit of a southwesterly bent.
Illinois 37's northern end is near Watson, just south of Effingham, at US Route 45:
Illinois 37 meets the eastern end at Illinois 185 in Farina:
At the tiny town of Whittington, Illinois 37 meets the eastern end of Illinois 154:
As Illinois 37 enters Benton, Illinois, Illinois 14 joins it from the east:
As Illinois 37 continues through the town square rotary in Benton, Illinois 14 is passed off to the west, and Illinois 34 spawns to start off going east:
Illinois 37 crosses Illinois 149 in West Frankfort...
In the heart of Marion, Illinois, Illinois 37 crosses Illinois 13:
North of Goreville, Illinois 37 meets the southern end of Illinois 148:
Illinois 37, after crossing under Interstate 24 (no access), crosses Illinois 146 few miles west of Vienna:
Illinois 37 meets the western end of Illinois 169, west of Karnak:
After passing through Mound City and Urbandale, Illinois 37 ends at US Route 51, at a point common to Illinois 3's southern terminus.