SBI Route 161 was Carlyle to Belleville. In 1941 IL-161 was dropped from Bartelso to Carlyle, and then extended east to IL-37. This replaced IL-182 from Centralia east. In 1964 this was extended west to East St. Louis, a part of this extension was US-50 at one time. IL-161 now runs East St. Louis to IL-37 in St. Clair, Clinton, and Marion Counties.
SBI Route 162 was Spring Valley to LaMoille. In 1938 this was changed to IL-89. In 1954 IL-162 was used on a road from Glen Carbon to Granite City, and the extended in 1965 to a junction with US-40 east of Troy. This extension had been Bypass US-40. IL-162 now runs US-40 to Granite City in Madison County.
SBI Route 163 was a spur from IL-1 east to Palestine in Crawford County. This was changed to IL-33 in 1937. In 1954 it was used from Millstadt into East St. Louis. This was also Bypass-US-50 until 1957 when Bypass US-50 was relocated. IL-163 now runs Centreville to Millstadt in St. Clair County.
SBI Route 164 was Pekin to west of Bloomington, now part of IL-9. In 1937 IL-164 was used on a road that had been IL-94A from Monmouth to Gladstone. This still exists there, and is in Warren and Henderson Counties.
SBI Route 165 was (and IL-165 still is) a road from Sibley west to a junction with IL-9, in Ford and McLean Counties.
SBI Route 166 was (and IL-166 still is) a road from east of Marion to New Burnside in Williamson and Johnson Counties.
SBI Route 167 was (and IL-167 still is) a road from US-34 near Galesburg to IL-180 near Victoria, in Knox County.
SBI Route 168 was Rapatee to Cuba. In 1941 this was changed to IL-97 when IL-97 was extended. IL-168 has not been used since.
SBI Route 169 was Shelbyville to Dalton City, now part of IL-128. In 1949 it was used on a road from IL-37 to US-45 in Pulaski and Massac Counties.
SBI Route 170 was Red Bud to Sparta. This was changed to IL-154 in 1937. In 1946 this was used on the former IL-186 south from US-6 at Seneca to IL-17 near Budd. In 1995 it was extended south to IL-23 on a previously unnumbered road. It currently runs Seneca to IL-23 north of Pontiac in LaSalle and Livingston Counties.
SBI Route 171 was Thomson to IL-78, which is now unnumbered. In 1946 this was used to replace IL-213 from Lyons to Summit. In 1967 IL-171 was extended south to Joliet, replacing IL-4A. In 1998 IL-171 was extended north to IL-72 in Park Ridge via First Av and Cumberland Av. (Also known as Pueblo Av in Chicago). IL-171 currently runs from Joliet to Park Ridge in Cook and Will Counties.
SBI Route 172 was Libertyville to Gurnee that became IL-63, and now is part of IL-21. In 1946 IL-172 replaced IL-226 on a "T" shaped route west from Prophetstown to the current IL-40, and the bottom leg north and south from Tampico. In 1974 the west leg to Prophetstown lost its number, and the route was then an inverted "L" shaped route. This is its current route, in Whiteside and Bureau counties.
I-172 runs from I-72 south of Quincy to US-24 north of Quincy. There it is being extended north towards Macomb and eventually Galesburg to meet up with I-74. There are about 16 miles built so far around Quincy. IL-336 was on this route previously, and is now used on the 4 lane divided section north of Quincy that isn't Interstate Standard.
SBI Route 173 was (and still is) Zion to what is now Machesney Park. From 1972 to 1994 this was also used on a part of the former IL-42 from the WI line south to this route. This was changed to IL-137 in 1994. IL-173 runs in Lake, McHenry, Boone, and Winnebago counties.Prior to the development of Machesney Park in the 1970's and 1980's IL-173 ran south into Rockford on Forest Hills Road.
SBI Route 174 was a short route northwest of Peoria from IL-40 (formerly IL-88) to IL-91 through Alta. It was removed in 1983 and the road has been unnumbered since. The number has not been used since.
Rumors have been heard of this being reserved for use on the freeway portions of US-34 and US-67 SW from Galesburg. It is more likely that this would become I-172 if the two projects connect. According to IDOT sources, there are no plans to connect these 2 routes with an Interstate, but rather a Multilane divided highway will be built.
SBI Route 175 was a tiny spur to Glasford from US-24. The number was pulled before 1935.
SBI Route 176 was Crystal Lake to Lake Bluff. In 1940 it was extended west to Marengo, replacing IL-67. It currently runs Marengo to Lake Bluff in McHenry and Lake Counties.
SBI Route 177 was New Minden to Okawaville. In 1937 it was extended east to Irvington on a part of the old IL-153. In 1967 it was extended east to Belleville on an old alignment of IL-15. Its current routing is Belleville to Irvington in St. Clair, Clinton and Washington counties.
SBI Route 178 was (and IL-178 still is) a road south from I-80 (was US-6) to Lowell in LaSalle County. Apparently it ran SW to US-51 (now IL-251) during the 1950's.
SBI Route 179 was a road from IL-18 near Lostant to IL-251 (was US-51) at Rutland. This route is now LaSalle County 44.
SBI Route 180 was (and IL-180 still is) near Galva to Williamsfield in Knox County.
I-180 is a spur serving a huge steel mill once operated by LTV (A major defense contractor) at Hennipin IL, about 13 miles. There is a 1 mile spur on this spur that is also part of I-180 that connects it with IL-29. This is one of the routes being considered for part of the long planned Chicago-Peoria Expressway, they would upgrade IL-29 between I-180 and IL-6's freeway at Peoria.

Route overview and markers

Updated 11-18-2007