Horizon High School is a public secondary institution located in Thornton, Colorado.

Horizon High School opened in 1988 to relieve crowding at Northglenn High School.

[4] Following rapid growth in Adams County throughout the 1990s, Horizon High School quickly filled to capacity and by 1999 the campus had 20 portable classrooms outside the school's main building.

[5] Originally, the school only had grades 10-12.

Horizon High School fields teams that compete in interscholastic competition in baseball, basketball, cross-country, football, golf, gymnastics, soccer, softball, swimming, diving, tennis, track and field, volleyball and wrestling.