U.S. Route 191 (US 191) is a north–south United States Highway within Arizona. The highway runs for 517 miles (832 km), the longest of any numbered highway in Arizona, from State Route 80 near Douglas to the Utah state line near Mexican Water. As it crosses the state, US 191 overlaps at various points: I-10, US 70, US 180, US 60, SR 61, I-40, SR 264, and US 160. Previously the route was designated as US 666 and SR 63.