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.
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
Route Number Oddities
has some strange number assignments, here are a few of
the stranger ones:
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
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.
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...
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.
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.
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.
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
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
Business-US-12, City-US-12, US- 14, US- 20, Business
US- 20, City-US-20,
30, Business-US-30, City-US-30, Alt-US-30,
32, US- 34, US- 54, US- 66
Alt-1, IL-4, IL-4A, IL-5, IL-6, IL-7, IL-21, IL-42, IL-55
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
following numbers are not currently used on State routes
in Illinois (Those shown in gray would not conflict with
current US or Interstate routes: