Illinois Highway Trivia

Origins

The original Illinois state highways were simply numbered in order of origination, and consisted of little more than numbers placed on poles of existing trails. Before that important routes had names, such as the "National Home Trails" or the "National Road"

---

SBI Routes

An organized system of numbering state highways started in 1918 with the first State Bond Issue (SBI) Routes, 1 thru 46. SBI Routes 47 thru 185 were authorized in 1924. Bonds were floated to pay for specific routes. SBI # 1 paid for Route 1, and so on. Remarkably, many of these numbers still exist on the original or nearby alignment. As the highway system grew the numbers were altered to accommodate new roads or extensions of older roads. When the US Highway System of Interstate Roads started to be posted in 1926, the US numbers were just tacked onto the existing IL/SBI number unless the US route was routed along a new route. In the 1930's the IL/SBI numbers were dropped when they were only a second number on a US marked road. Other IL (and US) routes were dropped over the years as the Interstates were built, and traffic patterns changed.

SBI Route numbers that were superseded by other routes, US or state routes were often reused. For example, SBI Route 68 was in part the current US-41. IL-68 is now an East-West road thru Cook and Kane Counties. (It actually ends at US-41 in Northbrook). SBI-19 was the current US-14, and IL-19 is now Irving Park Road from Chicago to Elgin.

SBI Numbers are still used for several purposes, even when they do not match the posted number. IDOT District maps still refer to SBI numbers on the various roads it maintains, along with other non-posted designations that refer to how the route was authorized. Bridge weight plates refer to SBI numbers instead of posted route numbers as well. If you look at a bridge plate along old US-66, you will see the route referred to as "SBI-4"

Other abbreviations seen on bridge plates and IDOT Maps include:

---

IDOT Maps

Any road considered a part of the Illinois Primary or Secondary Highway System will be shown on IDOT District Maps. These are amazing references to the state highway system, in that they show the origin of each portion of the states road system. They are of various sizes, depending on the district involved. The District 1 map (covers the Chicago area) is about 5 by 4 feet!

The Illinois Department of Transportation produces an Official Highway Map every other year (in odd years). These maps are also used by the Secretary of State (SOS) and Department of Community Affairs (DOCA), each agency providing a different cover and occasional message inside. For a definitive guide to IL (and other states) official highway maps go to the RMCA website.

I collect Official IL road maps for my research. If you have some you want to trade, send me an e-mail

---

Mileage Signs and

900 series "Route Numbers":

Illinois posts unique mileage signs on rural routes. These signs are square, with a white background, and a green circle containing a dividing line horizontal within the circle. The name of the county in which the sign is in is in the dividing line, and the number of the route is above the divider. The mileage from the county line is on the lower half of the circle. The mileage starts again at the next county line.

These signs are posted on most IL state and US posted highways in rural areas, at integer (whole number) mile points, and at rural features such as bridges, culverts, and intersections. Not all of these features have these signs, and they do not seem to be posted everywhere. No distinction is made as to the type of highway (State vs. US) except that rural Business routes (Business US-24 for example) will have "BUSN XX) in the Route Number area.

Some highways that have been realigned or replaced by a freeway have these signs also, even though they are no longer part of the numbered highway system. These roads are still maintained by IDOT, but have no route number. They are each assigned a number in the 900 series and this number only appears on these mileage signs. These signs are part of the rural referencing system. They are used for IDOT sign inventories, accident coding purposes, guardrail inventory, preparing road projects, and a few other things. Those signs are somewhat used for navigation. They run from south to north and west to east.

The 900 series numbers I know about include:

910 (The former IL-121 north of Lincoln, replaced by I-155)

911 (A former alignment of US-51 in Union County)

913 (A former alignment of IL-13 between Murphysboro and Carbondale)

 

---

Letter Appended Routes

Some IL routes had letter appended to them. These routes have been eliminated over the years by changing to regular numbers or removing the number altogether. The last one was IL-116A which became IL-117 in the early 1990's. These are considered Spurs or Alternates of the parent route, and letters used have been A,B,C, N (North), and S (South). These should not be confused with the US appendages or Alternate/City/Business Routes, as different rules were used. A few State routes had Alternate, City, or Business Routes in addition to the regular State route, often these were the old route thru towns when the new alignment was built outside town.

This table shows each letter appended state route in IL that I know of, and the current number if any. Each route is described individually elsewhere.

---

"Banner" Illinois Routes:

There were not many of these routes in IL, each that I know of are shown below. Each is described in detail in the narrative section.

Banner IL-xxx Routes	Current Number
	IL-394
	Truck Bypass IL-3
	None
	None
	None
	Business US-51
	Truck Bypass IL-64
	None
	Business US-51
	(Proposed) Alternate IL-159

3 Digit IL routes

There are many 3 digit IL route numbers. Most do not relate to a "Parent" route, but some do:

Original Number	Current Number	Notes
IL-138	IL-138	Became a spur off of the original IL-38 from Mt. Olive
IL-140	IL-140	Was used as a spur off of US-40, and was later extended on part of an old alignment of US-40.
IL-190	I-88	Was a spur off of I-90. (The original part of the East-West Tollway to Aurora)
IL-192	IL-192	Is an old alignment of IL-92
IL-194	I-90	Was a spur off of I-94. (This was the Kennedy Expressway west of the I-94/Edens Split)
IL-203	IL-203	Is an old alignment of IL-3
IL-242	IL-242	Is the current number on a road that had once been IL-142A.
IL-250	IL-250	Is an old alignment of US-50.
IL-251	IL-251	Is an old alignment of US-51.
IL-255	IL-255	Is an extension of I-255.
IL-267	IL-267	Is an old alignment of US-67.
IL-316	None	Was an old alignment of IL-16.
IL-336	IL-336, I-172	Is a spur of US-36 (now I-72). A former section of IL-336 is now I-172.
IL-351	IL-351	Is an old alignment of US-51.
IL-394	IL-394	Is a spur of I-94.
IL-594	I-190	Was a spur off of I-94.

---

Number Patterns

IL Numbered routes do not follow any other known pattern. The "Even/Odd" configurations of the Interstate and US systems do not apply for IL routes. Some routes in IL are multidirectional, in that they do not have ANY posted direction. Sometimes numbers are assigned because they sound good, or the route is related to another route, or because the number had once been assigned to a portion of the route.

There was a pattern of "Bunching" when SBI routes were numbered, and then later when numbers were reassigned. The area south of St. Louis has a bunch of highways numbered in the 140's, 150's and 160's dating from SBI days. Lake County has IL-131, 132, 134, and 137, which all were reassigned after the original routes bearing these numbers were renumbered.

---

IL Route Number Oddities

Illinois has some strange number assignments, here are a few of the stranger ones:

IL-137 in Lake County runs N-S from the WI line thru Waukegan and North Chicago, then heads due West to the Round Lake area. None of the IL-137 signs have a directional indicator on them anymore. This had been an E-W Route until it was extended north in the 1990's to cover a small freeway in Waukegan. Portions of the N-S leg was originally IL-42, and parts of the E-W leg were once IL-21. As far as I know, this is the only "J" shaped route in Illinois.

IL-172 today is weird enough in that it is an "L" shaped route from south of Rock Falls to Tampico and IL-92. In the 1940's this route was "T" shaped and extended west to Prophetstown. In 1946 IL-172 was used here in place of IL-226. Other "T" routes existed in SBI days, but few were used afterwards.

IL-38 was numbered that since it had a good sound! The route was the original US-30, also known as the Lincoln Highway west of Geneva. It became US-30-A (or Alternate US-30) after US-30 was rerouted south of the original road. After the Great Purge, the portion of US-30-A from Dixon to Bellwood became IL-38. Sound this out...

IL-40 now runs from Mt. Carroll to Peoria. This had been IL-88 for many years. When IL-5, the East-West Tollway, was changed to I-88, IL-88 had to change since it crossed I-88 near Rock Falls. In the 1930's, IL 40 existed from Sterling to Mt. Carroll. IL-40 disappeared when IL-88 was extended to Mt. Carroll in 1938. When IL-88 needed to be changed, a number used on a portion of it before was recycled. Former IL-80 is now IL-84, it too had to change because of an Interstate crossing it. When I-80 was built in the 1960's it crossed IL-80 near Rock Island, so they changed IL-80 to IL-84.

IL-54 had originally been where part of IL-83 is now. In the 1940's they extended US-54 from Pittsfield to Chicago as an alternate to US-66 via Springfield. After US-54 was removed from Pittsfield to Chicago during the Great Purge, IL-54 was applied from Springfield to Onarga.

IL-22 was originally a loop around the Chicago area that started in Waukegan, went south to Highland Park, west to Fox River Grove, northwest to Crystal Lake, south to Joliet, and to the Indiana line. It has since been cut back to Highland Park-Fox River Grove.

---

The Great Purge

From 1968 to 1974 many US and IL routes lost their numbers, were shortened (by removing the numbers, not ripping up pavement...) or changed from US routes to IL routes. I call this the Great Purge. The Great Purge occurred due to the substantial completion of some of the original Interstate Highways.

At one time Downtown Chicago had dozens of numbered US and State routes that ended or traversed it. Now there is only 1: US-41, although IL-19 and IL-64 still go thru to Lake Shore Drive, but north of the Loop. Routes that at one time or another came into the Downtown area of Chicago include:

US-12, Business-US-12, City-US-12, US- 14, US- 20, Business US- 20, City-US-20,

US- 30, Business-US-30, City-US-30, Alt-US-30,

US- 32, US- 34, US- 54, US- 66

IL-1, Alt-1, IL-4, IL-4A, IL-5, IL-6, IL-7, IL-21, IL-42, IL-55

---

Unused Numbers

Illinois has used every number under 186 for a state route. Over 186, most route numbers were chosen as a relationship to another route of some sort. (See "3 Digit State Routes)

The following numbers are not currently used on State routes in Illinois (Those shown in gray would not conflict with current US or Interstate routes:

Number	Current Number
IL-11	US-40
IL-12	US-50
IL-20	IL-120
IL-24	IL-29
IL-27	US-52
IL-28	US-34
IL-30	US-150, IL-91 and others
IL-36	US-36 and others
IL-39	US-150
IL-42	IL-137 in part
IL-44	US-52
IL-45	unnumbered (was IL-179 for a while)
IL-46	unnumbered
IL-51	US-45
IL-52	IL-83
IL-55	IL-56
IL-63	IL-68, IL-21 and IL-137
IL-65	US-34
IL-66	IL-126
IL-67	IL-176
IL-69	US-52
IL-74	IL-26
IL-77	IL-64
IL-79	IL-35
IL-79 (2)	US-36
IL-80	IL-84
IL-85	US-67
IL-86	IL-5, IL-92
IL-87	IL-26
IL-88	IL-40
IL-93	US-34, IL-91
IL-110	IL-16, IL-159, IL-15
IL-112	IL-159
IL-118	IL-23
IL-139	IL-14
IL-144	IL-149
IL-168	IL-97
IL-174	unnumbered
IL-175	unnumbered
IL-179	LaSalle Co. 44
IL-181	IL-33
IL-182	IL-161
IL-183	IL-154
IL-186	IL-170
IL-187	Never used
IL-188	Never used
IL-189	Never used
IL-190	I-88
IL-191	Never used
IL-193	Never used
IL-194	I-90
IL-195	Never used
IL-196	Never used
IL-197	Never used
IL-198	Never used
IL-199	IL-92
IL-200	Never used

 

 

 

 

 

Route overview and markers	Routes 1 thru 20	Routes 101 thru 120
	Routes 21 thru 40	Routes 121 thru 140
Illinois Highways Page Home	Routes 41 thru 60	Routes 141 thru 160
	Routes 61 thru 80	Routes 161 thru 180
	Routes 81 thru 100	Routes 181 thru 200
Updated 3-15-05	Send updates to n9jig@n9jig.com	Routes 200 and up