Canon-McMillan High School is the largest school building in the district, both geographically and by student population. Currently, about 2,000 students in grades 9–12 attend CMHS. The school was originally built and opened as Canon-McMillan Senior High School in 1958 with grades 10–12, and has been expanded and renovated in 1966, 1983, 1988, 1994, 2001–2003, and 2017–2019. CMHS has two gymnasiums (Main and Auxiliary), a natatorium, a weight room, and a mat room for wrestling practice as its athletic facilities. The school also has four outdoor tennis courts and formerly had an open playing field and outdoor exercise yard on its premises. An auditorium is also featured.