Oxnard Union High School District was established in 1901 and opened Oxnard High School in 1902. The district was formed by the elementary districts in the area it served in order to provide public education for grades 9 through 12.

Oxnard High School served all of the secondary students on the Oxnard plain and the Conejo Valley until 1956 when the district opened Adolfo Camarillo High School. The population growth of the area was reflected in the rapid addition of more schools: Hueneme High School in 1960; Thousand Oaks in 1962; Rio Mesa in 1965; Channel Islands in 1966; and Newbury Park in 1967. Frontier High School, a continuation school, was opened using existing facilities at the former Oxnard Air Force Base (now Camarillo Airport) in 1972.

In 1974, Thousand Oaks and Newbury Park High Schools became part of the newly established Conejo Unified School District, leaving this district with five comprehensive and one continuation high school. In 1995 the new Oxnard High School campus located on Gonzales Rd. opened its doors, discontinuing the use of the early 1900 era campus on 5th Street. Pacifica began serving students in 2001 and became the district's 6th comprehensive high school.