In the late 50's, much of the farmland in Northwest Boise was subdivided, and new neighborhoods appeared where none had been before. Students from these new homes attended North Junior High for a time, but the need for a new junior high school became paramount in 1960, when construction began on a new school adjacent to the foothills in this area. Hillside Junior High School opened in 1961; its setting is among the most attractive in the District, with the Boise Front mountains silhouetted in the background behind the school.

Hillside had over 600 students on opening day, but the school had not yet been completed, and some classes met in the cafeteria. The school population continued to grow and in 1968-69 fifteen classrooms were added to the school. The school is built around a courtyard which is used during the fall and spring as an outside classroom.

In the early 90's, growth in Northwest Boise caused the population of Hillside to swell. By 1995, over 900 students were enrolled, and portable classrooms dotted the land surrounding the school. Passage of a bond issue in February, 1996 allowed for the construction of a new junior high school on Gary Lane, Riverglen Junior High, several miles west of Hillside. This resulted in the reduction of the student body to a population of approximately 450. This has resulted in the removal of all but four of the portables. This has also alleviated serious crowding in the hallways and cafeteria. The staffing has also undergone modification, with a number of them now teaching at Riverglen.