IL 251 highlighted in red
|Maintained by IDOT|
|Length||135.32 mi (217.78 km)|
|South end||I-39 / US 51 / CR 8 in Hudson|
|North end||US 51 / IL 75 in South Beloit|
|Counties||McLean, Woodford, Marshall, LaSalle, Lee, Ogle, Winnebago|
Illinois Route 251 is a north–south state road that runs on the former alignment of U.S. Route 51 before Interstate 39 was built in central Illinois. It runs from U.S. 51 at the border with Wisconsin to I-39 and U.S. 51 south of Kappa. Illinois 251 is 135.32 miles (217.78 km) long.
Illinois 251 runs parallel to Interstate 39 and U.S. 51 for most of the length of I-39 in Illinois. Like Illinois Route 351, it can be considered a spur, loop or alternate of its parent route, U.S. 51. Illinois 251 terminates about 8 mi (13 km) north of the southern terminus of I-39.
The road parallels the east bank of the Rock River through Rockford, where the highway goes north on Eleventh Street, west on Harrison, north on Kishwaukee, west on Walnut then split between northbound Third and southbound Second through downtown Rockford. After downtown, both directions take the southbound lanes' Second Street name as a divided urban expressway (also badged as Martin Luther King Jr. Memorial Drive) for a couple of miles north of downtown Rockford. It stays Second Street through Loves Park, Machesney Park and Roscoe until its north endpoint at US 51 and Illinois 75 in South Beloit
Illinois 251 was established in 1982 when first segment of I-39 opened between Rockford and Bloomington. In 1992, the final segment of I-39 opened north of Bloomington. The remaining stretch of Former U.S. 51 became Illinois 251. The initial designation of I-39 was U.S. Route 51 until 1992.
|McLean||||0.0||0.0||I-39 / US 51 – Bloomington–Normal, Rockford||Southern terminus; I-39 exit 8|
|Woodford||El Paso||7.1||11.4||US 24 (West Main Street)|
|||15.2||24.5||IL 116 west||South end of IL 116 overlap|
|||16.2||26.1||IL 116 east||North end of IL 116 overlap|
|Marshall||||27.6||44.4||IL 17 west||South end of IL 17 overlap|
|Wenona||29.6||47.6||IL 17 east (Elm Street)||North end of IL 17 overlap|
|LaSalle||||34.6||55.7||IL 18 (North 13th Road)|
|Tonica||41.7||67.1||CR 54 (Ray Richardson Road, Ed Lambert Road)|
|||44.8||72.1||IL 71 / IL 351 north|
|||45.6||73.4||I-39 / US 51 – Bloomington–Normal, Rockford||I-39 exit 52|
|Illinois River||49.6||79.8||Peru Bridge|
|Peru||49.8||80.1||US 6 – LaSalle, Spring Valley||Interchange|
|||52.5||84.5||I-80 – Moline, Rock Island, Joliet||I-80 exit 75|
|||55.7||89.6||CR 33 (North 33rd Road)|
|||59.7||96.1||US 52 east (North 37th Road)||South end of US 52 overlap|
|Mendota||65.1||104.8||US 34 (Washington Street, Walter Payton Memorial Highway)|
|66.1||106.4||US 52 west||North end of US 52 overlap|
I-88 / IL 110 (CKC) (Ronald Reagan Memorial Tollway) – Chicago, Moline, Rock Island
|I-88 exit 76|
|Rochelle||93.1||149.8||IL 38 west / Lincoln Highway (Lincoln Avenue)||South end of IL 38 overlap|
|94.0||151.3||IL 38 east / Lincoln Highway (May Mart Drive)||North end of IL 38 overlap|
|Davis Junction||105.8||170.3||IL 72 (Chicago Avenue)|
|Winnebago||Rockford||114.0||183.5||US 20 (Rockford Bypass) – Freeport, Belvidere||Interchange|
US 20 Bus. (1st Avenue, Jefferson Street)
|118.7||191.0||Whitman Street Bridge||Interchange|
|120.1||193.3||Auburn Street, Spring Creek Road||Interchange|
|120.6||194.1||Forest Hills Road||Northbound exit and southbound entrance|
|Machesney Park||125.7||202.3||IL 173 east (West Lane Road)|
|Roscoe||132.8||213.7||CR 76 (Prairie Hill Road)|
|Rockton||133.8||215.3||CR 9 (Rockton Road)||Interchange|
|South Beloit||135.32||217.78||US 51 / IL 75 (Gardner Street)||Northern terminus|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi|
- Carlson, Rich. Illinois Highways Page: Routes 200 thru end. Last updated April 15, 2005. Retrieved May 12, 2006.
- Illinois Technology Transfer Center (2006). "T2 GIS Data". Retrieved 2007-11-08.
- AARoads. Interstate 39 @ Interstate-Guide.com.
- Google (March 12, 2017). "Overview Map of IL 251" (Map). Google Maps. Google. Retrieved March 12, 2017.