William S. Hart High School is a four-year public high school in the neighborhood of Newhall in the city of Santa Clarita, California, United States. Founded in 1945, it is the oldest high school in the Santa Clarita Valley. Named for local cowboy actor William S. Hart, it is part of the William S. Hart Union High School District.

Newhall is the southernmost and oldest community in the city of Santa Clarita, California. Prior to the 1987 consolidation of Canyon Country, Saugus, Newhall, and Valencia into the city of Santa Clarita, it was an unincorporated area. It was the first permanent town in the Santa Clarita Valley.