State Highway 121 is a 30.425 mile (48.96 km) long state highway in the U.S. state of Colorado.

The route, also known as Wadsworth Boulevard, Wadsworth Bypass, and Wadsworth Parkway, starts at the junction of State Highway 470 and State Highway 75 in unincorporated Jefferson County and ends at the junction of US 36, US 287, and State Highway 128 in Broomfield. State Highway 121 passes through portions of southwest Denver County

The name Wadsworth comes from Benjamin Franklin Wadsworth, one of the founders and first postmaster of Arvada. In northwest Arvada, Wadsworth Boulevard passes over Hackberry Hill at the site where a landmark hackberry tree, for which the hill was named, stood before it was cut down to make room for the highway in 1937.