U.S. Route 73 starts at I-70 in Kansas City. It goes along with U.S. Route 24, U.S. Route 40, and K-7. Two miles north of its endpoint, US 24 and US 40 turn west; US 73 continues north with K-7. It goes north with K-7 through Lansing, where it intersects K-5. US 73 and K-7 then go through Leavenworth. It goes northwestern from Leavenworth. It meets K-192 near Easton. At Atchison, it turns west. At Atchison, K-7 ends. US 73 goes along with U.S. Route 59. It goes west. It then turns northwest near Lancaster at its intersection with K-9. It goes through Huron. It goes along with K-20 near Everest. It goes west into Horton, and it intersects U.S. Route 159. The two highways go north together, and they meet U.S. Route 36 at Hiawatha. After going northwest through Reserve, US-73 and US-159 turn north and enter Nebraska.