State Route 126 is a state highway in the U.S. state of California that serves Ventura and Los Angeles counties. The route runs from U.S. Route 101 in Ventura to Interstate 5 at the Castaic Junction-Santa Clarita border through the Santa Clara River Valley. The highway is an important connector highway in Ventura County, and serves as an alternate route into the Santa Clarita Valley, and the San Fernando Valley area of Los Angeles and the High Desert of Antelope Valley.