US-400 goes east through several small towns before turning southeast to go through the Fredonia area. It intersect US-75 at Neodesha. After going along with US-75, it turns east. It intersects U.S. Route 169 near Morehead and then US-59 near Parsons. Then it intersects US-69 south of Pittsburg. It then turns south with US-69. At Crestline, it follows US-69A south to Riverton. US-400 then turns east with US-166 at Baxter Springs. The two highways go eastward into Missouri.