Illinois 150 generally runs southwest to northeast, but is marked as an east–west route. From the Chester Bridge, it runs northeast through Chester, briefly overlappingIllinois Route 3. A longer concurrency takes place further northeast at Illinois Route 4. East of Percy, Illinois 150 turns north to Illinois 154. In Chester, it is named State Street.
In 1937, the changes from Illinois 150 to Illinois 3 and 4 took place (the change to Illinois 4 initially was a change to Illinois Route 43). Illinois 150 then was extended east and west (replacing what was then Illinois Route 151) to its current length.[3]