State Highway 66 is a 22.7 mi (36.5 km) long east-west state highway in Boulder and Weld counties in Colorado. The highway extends from the foothills of the Rocky Mountains at a junction with U.S. Highway 36 southeast of Lyons, proceeding east through the northern edge of Longmont, to Platteville where it ends at U.S. Highway 85. Although a number of western states retain their "state highway 66" as the decommissioned U.S. Route 66, the "Mother Road" did not run through Colorado, and State Highway 66 has no connection to the famed Historic Route 66.