K-126 is a mostly east–west state highway located entirely within Crawford County in southeastern Kansas. Its western terminus is at U.S. Route 400 (US-400) just south of McCune, and its eastern terminus is the Missouri state line where it continues as Route 126. Along the way the highway passes through the city of McCune and also the city of Pittsburg, where it intersects US-69 and US-160. On October 11, 1940, the section from Pittsburg east to the Missouri state line was designated as K-104. On September 30, 1943, US-160 was realigned to follow K-126's current route from US-400 to Pittsburg, K-104 was moved to a highway from K-7 east to US-69, and the highway from Pittsburg east to the Missouri line was designated as K-126. Then in 1958, US-160 was realigned to go directly east from south of McCune to US-69 and at that time K-126 was extended along the old US-160 through McCune to end at the new US-160 (modern US-400). Route description K-126 begins at an intersection with US-400 and heads northward; south of this intersection, the roadway continues as Northwest 100th Street. The highway passes the small city of McCune on its eastern limit, then meanders slightly to the northwest before turning north again. It continues in this direction for about and then curves due east. Afterward, K-126 crosses Lightning Creek and continues east through mostly open farmlands and pastures toward Pittsburg. Approximately east of Lightning Creek, the route intersects K-7, then crosses the BNSF Railway. K-126 continues east past the railway through flat, open plains. It then enters a lightly wooded area scattered with several small ponds and crosses Second Cow Creek en route to Pittsburg. Just inside the city limits of Pittsburg, K-126 crosses First Cow Creek. East of the creek is a four-lane highway that carries the US-69 and US-160 designations. K-126 intersects this road, then continues eastward into the city; the route is known as 4th Street inside the city limits. It serves a residential area in the western section of the city, then passes a library and enters the downtown section. Here, it meets U.S. Route 69 Business (Broadway Street), then continues farther east. After leaving the downtown section of Pittsburg, K-126 passes over a railroad that serves both the South Kansas and Oklahoma Railroad and the Kansas City Southern Railway. The road runs south of a city park, then heads through