Illinois Route 140 is an east–west highway with its western terminus at Alton

Alton, Illinois

Alton is a city on the Mississippi River in Madison County, Illinois, United States, about north of St. Louis, Missouri. The population was 27,865 at the 2010 census. It is a part of the Metro-East region of the Greater St. Louis metropolitan area in Southern Illinois...

 and its eastern terminus at Illinois Route 185

Illinois Route 185

Illinois Route 185 is an east–west state road in the south-central portion of the U.S. state of Illinois. Its western terminus is in Taylor Springs at Illinois Route 127, and the eastern terminus is at Farina at Illinois Route 37. This is a distance of ....

 and U.S. Route 40

U.S. Route 40

U.S. Route 40 is an east–west United States highway. As with most routes whose numbers end in a zero, U.S. 40 once traversed the entire United States. It is one of the original 1920s U.S. Highways, and its first termini were San Francisco, California, and Atlantic City, New Jersey...

 in Vandalia

Vandalia, Illinois

Vandalia is a city in Fayette County, Illinois, United States, northeast of St. Louis, on the Kaskaskia River. From 1819 to 1839 it served as the state capital of Illinois. Vandalia was the western terminus of the National Road. Today it is the county seat of Fayette County and the home of the...

. It also overlaps Illinois Route 111

Illinois Route 111

Illinois Route 111 is a north–south state road in southwestern Illinois. It runs from Short Street in Centreville to Illinois Route 104 in Waverly. This is a distance of .- Route description :...

 in Alton and Illinois Route 127

Illinois Route 127

Illinois Route 127 is a north–south highway in central and southern Illinois. Its southern terminus is at Illinois Route 3 near Olive Branch and its northern terminus at Interstate 55, along with the southern terminus of Illinois Route 48 in Raymond. This is a distance of .- Route description...

 in Greenville

Greenville, Illinois

Greenville is a city in Bond County, Illinois, United States, east of St. Louis. The estimated population as of July 2009 is 7,284. The population was 6,955 at the 2000 census. It is the county seat of Bond County....

. This is a distance of 52.05 miles (83.77 km).

Although this route may appear to be a derivative of US 40, it does not follow any of the old US 40 alignment except for a portion of the Historic National Road in Fayette County from US 40 to Vandalia. IDOT has since truncated the eastern end of IL 140 to the town of Mulberry Grove with the intersection of US 40.

In 2007 IDOT decommissioned the portion of Route 140 from near the Bond and Fayette County line at Mulberry Grove, east to Vandalia. While that section of highway is no longer marked for Route 140, the state still maintains it's Historic National Road signage.