In Harrisburg, Illinois 34 formerly ran the length of Main Street where it at one time sharply turned at Raymond St, then crossed a five way stop between U.S. Route 45, Sloan St, and Illinois Route 145 where it overlapped.

Illinois Route 34 serves as a main north–south road for towns located in the eastern portion of the Shawnee National Forest.

SBI Route 37 ran from Harrisburg to Elizabethtown, currently located northeast of Rosiclare on Illinois 146.

There was also a spur west to Golconda, which is located southwest of Rosiclare on modern-day Illinois 146.

In 1937, the road was extended northwest to Benton and its southern end moved to the Rosiclare ferry,[3] which stopped operating in the mid 1960s.