The largest population centers along the route are Macomb, Rantoul, and Danville.

Additionally, US 136 contains what is perhaps one of the longest straight stretches of a U.S. Highway east of the Mississippi River, running nearly 86 miles (138 km) without any deviations from north of Easton to just west of Rantoul.

In Carthage, US 136 then runs concurrently with IL 94 until it reaches a diamond interchange east of the city.

Then, it turns southeast north of Adair and then south and then east at Table Grove.

It then meets IL 29 from the south where it travels concurrently until it leaves northward near San Jose.

At Armstrong, it turns south and then back east which overlaps IL 49.

[2] In the middle of Henning and Alvin, US 136 turns south which overlaps IL 1.

In 1939, a part of Illinois Route 10 (IL 10) moved its western terminus from Decatur to Keokuk, Iowa.