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.