State Route 66 (SR 66) is a surface road in the U.S. state of Arizona in Mohave and Coconino Counties. In 1914, the road was designated "National Old Trails Highway" but in 1926 was re-designated as U.S. Route 66. In 1985, U.S. Route 66 was dropped from the highway system. Parts of the highway were either absorbed into I-40, turned over to the state (SR 66), or turned over to Yavapai County.