Given that Route 66 was planned as a major transcontinental highway, it soon became apparent that minor regional highways along 66’s route would benefit from being upgraded to Federal status as branch routes of the parent highway. US Highway 166 was the first of the five (later six) branches to be specified in the Joint Board of Interstate Highways’ plan issued in 1925.
When the American Association of State Highway Official (AASHO, now AASHTO) approved the creation of US 166 in November 1926, its original routing was entirely in southeastern Kansas. The highway began at a junction with US 66 in Baxter Springs, scene of a violent Civil War conflict in 1863 between the Northern forces of James G. Blunt and a band of Confederate guerillas commanded by William Quantrill .
US 166 continued westward through Coffeyville, Arkansas City, and the Flint Hills country, to the village of South Haven and a total of nearly 170 miles. There, the route ended at a junction with US Highway 81, a main north-south highway running from the Dakotas down to Laredo, Texas.
The western terminus of the highway has not changed and today remains at South Haven. Its eastern terminus, however, has changed twice. The first change occurred in 1945, when an extension into the state of Missouri routed the highway through Joplin to a new terminus in Springfield. The second happened in the 1960s with the construction of Interstate 44 through the state. US 166 was truncated back to nearly its original routing, to a point just southwest of Joplin. There, it ends at an interchange with Interstate 44 and US Highway 400. With the demise of its parent, Route 66, US 166 has become a highway of local interest, passing through territory that was once Cherokee Indian land.
Droz, Robert V., "Sequential List of US Highways", US Highways From US 1 to US 830. July 2003. <http://www.us-highways.com/us1830.htm> (February 2004)
LASR, Flint Hills Country, KS. 2003. <http://www.lasr.net/pages/highway.php?Region_ID=KS01&Highway_ID=KS01us166
> (February 2004)
Moore, Bob and Grauwels, Patrick. Route 66: The Illustrated Guidebook to the Mother Road. Williams, Arizona: Roadbook International, 1998
Sanderson, Dale, "End of US Highway 166", US Highway Ends. January 2002. <http://www.geocities.com/mapguy_annex/HwyEnds/End166/end166.htm> (February 2004)
Weingroff, Richard F., "U.S. 666: Beast of a Highway?", Federal Highway Administration Highway History. June 2003. <http://www.fhwa.dot.gov/infrastructure/us666.htm> (February 2004)