IL-203 was applied to an old alignment of IL-3 in 1964 from Hartford to East St. Louis. The north end was later shortened to end at I-270.
IL-213 was used until 1946 on what is now IL-171 from Summit to Lyons. Why and how it got this number is anyone's guess.
IL-226 was the original number on IL-172. This had been SBI-82 until the 1930's when it was changed to IL-226. IL-226 was changed to IL-172 in 1946.

IL-242 was first used in 1974 on a road from Wayne City to McLeansboro in Wayne and Hamilton counties. This had been the following routes:

  • IL-142A, 1926 to 1942,
  • IL-147, 1942 to 1947,
  • IL-142, 1947 to 1974,
  • IL-242, 1974 to present.
IL-250 was applied in 1965 to 2 old sections of US-50 from Lawrenceville to Sumner and Olney to Noble. These routes had been Alternate-US-50 from 1947 to 1961, and unnumbered from 1962 to 1964. The section of US-50 between Sumner and Olney carries the IL-250 number as well.
IL-251 was applied on old portions of US-51 after it was rerouted onto what is now the Northwest Tollway from the WI line to the US-20 bypass SE of Rockford in the early 1970's. As US-51 was moved to a new freeway during the 1980's and 1990's, IL-251 took over the old road to its current route from the WI line to north of Bloomington, in Winnebago, Ogle, Lee, LaSalle, Marshall, Woodford, and McLean Counties.
I-255 is the eastern and southern part of the loop around St. Louis, running from I-270 near Pontoon Beach, crossing I-55 at Collinsville and the Mississippi River at the Jefferson Barracks Bridge and ending at I-55/I-270 near Mehlville MO. All but the last 2 miles of the entire 35 miles of I-255 are in IL. The northern has been extended to near Alton as IL-255.

IL-255 is used on the extension of the Interstate-255 route north of I-270, from Pontoon Beach towards Alton. The road may end up eventually as some Interstate number. The new extension of I-255 opened in October 1998 (to IL-143). There is talk of extending this road further north to IL-140 starting in 1999. The ultimate end will likely be at US-67 near Godfrey. This is known locally as the Alton Bypass.

In 2005 the route was be completed to IL-140 at Bethalto. Next it will be extended further north to the Godfrey area, then to Jerseyville along US-67. This should be completed by 2015.

IL-267 was applied in 1965 on the former Alternate US-67 from near Murrayville to Godfrey. Prior to the 1950's this was US-67.

In 2001 US-67 and IL-267 were swapped so that IL-267 now runs south from Murrayville to Medora in Morgan, Greene and Jersey Counties. (South of Medora IL-111, which was a second number on this road, was retained by itself.)

I-270 runs from Troy IL to near Arnold MO, as the north and west sides of a loop around St. Louis. The rest of the loop is I-255. I-270 crosses the Mississippi River near the old Chain of Rocks bridge location, and has about 15 miles (of 48 total) in IL. This provides a good way to get around St. Louis, but the traffic is even worse here sometimes than going thru town. It is often easier to just drive straight thru St. Louis than fight the suburban traffic on the Loop, depending on bridge traffic

I-280 is the western bypass around the Quad Cities, from I-80/I-74 at Colona IL to I-80 in Davenport IA. The eastern 6 miles are multiplexed with I-74.

I-290 is the Eisenhower Expressway, from I-90 downtown Chicago to I-90 at Schaumburg (Woodfield), about 32 miles. West of the Tri-State it is commonly known as the "Extension" This route was once I-90 from the Loop to I-294, and was renumbered I-290 after it was extended to Schaumburg.

The Ike was built from 1955 thru 1960 and extended to the NW Tollway by 1972.

I-294 is the Tri-State Tollway from Deerfield to Lansing, meeting I-94 at both ends. This is about 53 miles long. This was once marked on some official maps as Toll-US-41, but it is unknown whether signs were ever posted as such.

The Tri-State is I-94 from the WI line to Deerfield, and I-80 from the IN line to the split near Hazelcrest.

The Tri-State was completed in 1958.

IL-316 was used on an old alignment of IL-16 from Mattoon to Charleston in 1963 after IL-16 was relocated to a new highway. IL-316 was removed in 1981, and the route is currently unnumbered.

US-330 ran from US-30 near Dyer (in what is now Lynwood) to Geneva until it was replaced by Alternate-US-30 in 1942. Routing was Glenwood-Dyer Road north from US-30 to torrence, Torrence north to 95th, then west to Stoney Island to Marquette, west to South Park (now MLK), and north to Roosevelt (12th St). It followed Roosevelt Road west to Geneva where it crossed the Fox River then north on what is now IL-31 thru Elgin to US-14 (now IL-72) at West Dundee.

In 1937, when the new routing for US-30 west of Aurora was complete, US-330 was used on the old US-30 west of Aurora, and IL-31 replaced US-330 north of here. When US-30 ran thru DeKalb (On the current IL-38) it came up for a short while from Aurora to Geneva and then headed west from Geneva. See US-30 for more details. (10-15-2006)

IL-336 is the extension of Interstate 172 north from the Quincy area. IL-336 had originally been used on what is now I-172, a spur off the Central Illinois Expressway that is currently being extended into Missouri. When the portion of IL-336 south of US-24 was changed to I-172 in the mid 1990's, the portion north of US-24 (which is not Interstate standard) remained IL-336. Construction of the "Super 4" roadway continues north from US-24 towards Carthage. In 2005 IL-336 is 4 lanes to near Bentley, a couple miles south of Carthage. Land acquisition and utility relocation is underway from south of Carthage to Macomb.

The eventual corridor is Quincy to Galesburg, via Carthage and Macomb with an eye on Peoria. At this time IDOT does not plan on making the route north of US-24 Interstate Standard, so it will remain IL-336 for now. Should this be upgraded to Interstate Standard it would likely become I-172 as an extension of that route. The same corridor south and west from Galesburg is partly Interstate Standard (at least to Monmouth) and there had been rumors of this part becoming I-174, but that seems to have been just a rumor. The entire corridor consists of I-172 north from I-72 (near Hull) to it's end at US-24, then north on IL-336 to it's current end at IL-61 near Mendon, then north with the new construction to near Bowen, and then to Carthage with an upgrade to IL-94. US-136 will be upgraded to a "Super Four" to Macomb, and meet with the current US-67 "Super Four". (The portion of US-67 around Roseville was completed in 2003.) Initial plans call for Mendon to Bowen to have 2 lanes paved, but the entire 4 lane right of way graded for eventual expansion to 4 lanes.

IL-351 was first applied in 1966 to an old section of US-51. This route had been Business-US-51 1963 to 1966 and US-51 before 1963. This is in LaSalle County, east of the city of LaSalle.

I-355 runs from I-80 near New Lenox north to I-290 at Itasca (about 30 miles), and was known as the North-South Tollway. The north part, from I-55 to I-290 was opened in 1989. The southern section from I-55 to I-80 was opened on November 11, 2007 and the entire I-355 was renamed as the Veterans Memorial Tollway.

The north extension to Grayslake is also in the planning and ROW acquisition stage (See IL-53).

IL-390

IL-390 was assigned in October 2013 as the new number for the Elgin-O'Hare Expressway, both the existing roadway as well as the east )into O'Hare Airport) and west (Towards Elgin) extensions.

(10-29-13)

IL-394 is the current number on an expressway that heads south from I-80/I-294. It was built as IL-1 in 1956 and the old IL-1 was changed to Alternate-IL-1. When the expressway was changed to IL-394, the old road became IL-1 again. Some people and maps mistakenly call this Interstate 394. If the airport at Peotone is ever built, this could become I-394. I-394 has never existed in IL, but the number is often misused as the extension south from I-94/I-80 from Lansing. This is properly known (and posted) as IL-394. This was once IL-1, and the original IL-1 became Alternate-IL-1. When IL-394 was posted Alternate-IL-1 reverted to IL-1.

I-394 has never existed in IL, but the number is often misused on maps as the extension south from I-94/I-80 from Lansing. This is properly known (and posted) as IL-394.

If the Peotone Airport is ever built this could become I-394, but this is unlikely for at least several years. Maps show the location of the proposed airport at the SW quadrant of the IL-394/IL-1 intersection.

US-430 ran from Geneva to Richmond on what is now IL-31. It was pulled after only a couple years, around 1935. It was entirely within IL. See US-30 for more details
US-460 originally ran from Louisville KY east to Norfolk VA. In 1947 in IL it replaced the then IL-13 from St. Louis to Freeburg, IL-110 to Nashville IL, IL-142 to McLeansboro, and IL-14 to IN near Crossville. In 1974, it was replaced by IL-15 east to Mt. Vernon, IL-142 reappeared to McLeansboro, and IL-14 reappeared on it's old alignment.
I-474 is the southern bypass around Peoria. It extends for about 15 miles from I-74 west of Peoria, to I-74 in East Peoria. Just east of the east end of I-474 is I-155 which heads south to Lincoln. IL-6 is the north extension of I-474 west of Peoria.
I-494 was shown on some maps as a second number on US-41 in Chicago (Lake Shore Drive), and was also planned for the Crosstown Expressway that was planned for Chicago in the 1970's but never built. This would have followed IL-50 south to Midway Airport, then to the Chicago Skyway. It is unknown whether this number was ever actually posted on LSD.
IL-594 was used from the Tri-State Tollway (I-294) into O'Hare Airport until about 1980 when it was changed to I-190.
I-594 was once rumored to be considered for the northward extension of the IL-53 expressway to meet the Tri-State Tollway at IL-120. This project is currently known officially as "FAP 342", and small green signs mark locations where this route may cross other roads in Lake County.

Route overview and markers

Updated 10-29-2013