Route information | ||||
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Maintained by IDOT | ||||
Length | 14.43 mi[1] (23.22 km) | |||
Existed | 1924–present | |||
Major junctions | ||||
South end | US 45 in New Burnside | |||
North end | IL 13 in Pittsburg | |||
Location | ||||
Country | United States | |||
State | Illinois | |||
Counties | Johnson, Williamson | |||
Highway system | ||||
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Illinois Route 166 (IL 166) is a 14.43-mile-long (23.22 km)[1] north–south state road in southern Illinois, United States. The route runs from its southern terminus at U.S. Route 45 in New Burnside to its northern terminus at Illinois Route 13 east of Marion. Route 166 serves the counties of Johnson and Williamson. It is maintained by the Illinois Department of Transportation (IDOT).