Illinois Road Network

By | October 13, 2022

Illinois has a dense road network, largely divided into a grid. The underlying road network opens up all agricultural areas and these roads are often asphalted. Major highways are mostly two-lane, with only a small number of state highway and US highway corridors having 2×2 lanes, a contrast to neighboring Indiana. Illinois, on the other hand, does have a large network of Interstate Highways.

Road management

The state highway authority is the Illinois Department of Transportation, abbreviated IDOT. IDOT operates 29,242 miles of road, including 3,516 miles of Interstate Highway, the third largest network of Interstate Highways in the United States. The state also operates 7,796 bridges.

IDOT has its origins in the Illinois State Highway Commission that was established in 1905. In 1913 this was expanded to the Illinois State Highway Department, but already in 1917 it was absorbed into the Department of Public Works and Buildings. In 1972, the current Illinois Department of Transportation was established.

  • Bittranslators: State overview of Illinois, including geography, economy, population and history as well as introduction to major cities of Illinois.

Interstate Highways

Illinois is a major transit state in the United States. Interstate 80 is an east-west route from Moline to Chicago, and is also the busiest truck corridor in the country with up to 40,000 trucks a day passing through Chicago. Interstate 94 here is a north-south route that connects Chicago to Milwaukee in Wisconsin. Interstate 90 connects the Chicago metropolitan area with Rockford and points further north. Interstate 88 in Illinois connects Moline to Chicago. Interstate 74 forms a diagonal east-west route between Moline, Peoria, and Danville at the border with Indiana. Interstate 72 forms an east-west route in the middle of the state, between Quincy and Champaign, and also serves the state capital Springfield.

Interstate 70 connects the metropolitan area of St. Louis with Indianapolis, and Interstate 64 connects St. Louis with southern Indiana. Interstate 24 is the southernmost east-west route, connecting the south with Kentucky.

The number of north-south routes is somewhat more limited, with Interstate 39 connecting central Illinois to Rockford, and Interstate 55 connecting St. Louis to Chicago. Interstate 57 is a long-haul road from Memphis to Chicago, bypassing all major cities in the state.

Most highways are, of course, around Chicago and St. Louis, but Illinois has a well-covered highway network, connecting all major places with highways. The state has a striking number of main routes of Interstate Highways, especially given the relatively limited size of the state. The underlying road network is extensive with many 2×2 main routes, both US Highways and State Routes.

  • Deluxesurveillance: Nickname of Illinois as The Prairie State. Also covers geography, history, economy, politics and administration of the state.

US Highways

A dense network of US Highways traverses Illinois. Most US Highways outside the cities are two-lane roads. A small number of corridors have been constructed as a 2×2 divided highway, such as US 20 west of Rockport, US 51 between Decatur and Bloomington, and US 67 between Macomb and Monmouth. The small share of 2×2 US Highways is because all places of any size are already served by Interstate Highways. Partly for this reason, relatively few corridors remain on which a lot of long-distance traffic is handled. Most bridges over the Mississippi River in western Illinois are US Highways.

State highways

The state highways are numbered in a series from 1 to 186 and some higher numbers are also assigned. The numbering originated in 1918 when the State Bond Issues (SBI) routes were established. In 1924, the system was further expanded, this is still the basis of current road numbering in Illinois. State highways almost always have a secondary character because of the dense network of Interstate Highways and US Highways. Only a few routes have been developed as 2×2 divided highway , often as approach roads to larger towns.

Some state highways have been developed as freeways;

  • IL 53: Schaumburg – Arlington Heights (Chicago)
  • IL 255: Granite City – Alton
  • IL 390: Elgin – O’Hare Expressway (Chicago)
  • IL 394: Bishop Ford Freeway (Chicago)

Toll roads

There are several toll roads in Illinois. The primary toll road operator is the Illinois State Toll Highway Authority (ISTHA), often abbreviated as the Illinois Tollway. The toll roads are all located in the northeast of the state, in the wider Chicago area. The Chicago Skyway is owned by the City of Chicago but under concession to the Skyway Concession Company.

  • Jane Addams Memorial Tollway (I-90)
  • Veterans Memorial Tollway (I-355)
  • Ronald Reagan Memorial Tollway (I-88)
  • Tri-State Tollway (I-80, I-94, I-294)
  • IL 390

A rest area along a toll road is called an “oasis” in Illinois, a unique designation within the United States.


Although Chicago was one of the largest cities in the United States early on, construction of the highway network started quite late here, unlike New York City or Los Angeles. In 1950, the first freeway opened, part of what is now I-80 through Chicago’s southern suburbs. In 1951, the Edens Expressway opened in northern Chicago, and during the 1950s, a series of toll roads in the Chicago area opened to traffic. Much of its construction predates the creation of the Interstate Highway system in 1956.

After the creation of the Interstate Highway system, highway construction progressed very quickly in Illinois. Priority was given to Interstate 80, which had already been completed in the mid-1960s, Illinois’ first long-haul toll-free highway. The construction of I-55 also went smoothly, and mostly involved the conversion of the already existing US 66, although some parts were not opened until later in the 1970s. Finally, in the 1960s, priority was given to Interstate 57, which serves few larger towns in Illinois. This highway was completed in the early 1970s. I-64 and I-70 were also completed in the early 1970s.

Later in the 1970s, I-74 was completed, and I-72 between Springfield and Champaign. I-24 was also built during that time, so that in the late 1970s Illinois had an extensive network of Interstate Highways, one of the densest networks in the United States. The largest construction project of the leaner 1980s was the construction of I-39 through the north of the state, which was largely completed between 1984 and 1992. In 1991, the western portion of Interstate 72 opened to traffic. In 1992, I-155 was also opened. After that, no new highways were opened for a long time. The most recent significant opening was I-355 in the Chicago area in 2007.

Illinois Road Network