K-51 is an approximately 79-mile-long (127 km) east–west state highway in the southwestern part of the U.S. state of Kansas. K-51 begins at the Colorado state line as a continuation of County Road M and travels eastward through portions of Morton, Stevens, and Seward counties before ending at U.S. Route 83 (US-83) north of Liberal. Along the way, it runs concurrently with US-56 from Rolla to Hugoton. Although K-51 travels through mostly rural farmlands, it does pass through the cities of Richfield, Rolla and Hugoton. The highway is also a two-lane road most of its length with the exception of short sections within Rolla and Hugoton, where it is four lanes.