The William S. Hart Union High School District (commonly referred to simply as the Hart District) is a school district in the Santa Clarita Valley of Los Angeles County, California. It serves all of the valley's high school students (grades 9-12) and most of its junior high school students (grades 7-8). As of 2019-20, the total number of enrolled students (in 16 schools) was 23,968. The district's superintendent is Mike Kuhlman. The district is named after William S. Hart, one of the first western film stars, who lived in Newhall and was a local benefactor. The region served by the Hart Dustruct is also served by the Sulphur Springs, Saugus, Castaic, and Newhall elementary school districts.