Chaffey Joint Union High School District is a 9–12 school district located in San Bernardino County, California, United States that serves the communities of Ontario, Montclair, Rancho Cucamonga, and portions of Fontana, Upland, Chino, and Mount Baldy.

Ironically, the university abandoned the agricultural school while Chaffey was away in Australia, so he pursued litigation and eventually won.

Funds from Measure X, a $128 million General Obligation Bond, allowed the district to build additional schools.

On September 10, 2013, ground was broken on the first significant project to be paid for under the bond, a two-story classroom annex at Ontario High School.

Starting with the Class of 2017, all eight comprehensive high schools hold their annual graduation ceremonies at the football fields located in each of the campuses.