The origins of the school began in November 1983 when Metropolitan Separate School Board (the forerunner to the
Toronto Catholic District School Board) and the
Archdiocese of Toronto jointly launched a new secondary school to serve northern Etobicoke. With overcrowding at
Father Henry Carr,
Don Bosco and
St. Basil, the MSSB recommended in a February 1984 meeting that the name, Monsignor Percy Johnson, be adopted. On September 4, 1984, the new Monsignor Percy Johnson school was opened in the facilities of the former Rexdale Junior School. Two years later, the school moved into the former Heatherbrae Middle School on Kipling Avenue, built in 1959, which was closed by the
Etobicoke Board of Education in June 1985. Throughout its early years Johnson had classes inside a middle school which had features in Etobicoke board standards that Toronto Catholic high schools did not have such as the gymnatorium, cafeteria, and a field of portable classrooms. Due to the size of the gym, home games were relocated elsewhere. In 2004, the TCDSB purchased Heatherbrae from the
Toronto District School Board. The old Heatherbrae school was demolished in 2005 and the replacement Johnson building was reconstructed until its completion in 2007, in which the new school opened for classes on September 4 that year. During construction, the student body was relocated to
Regina Pacis on Finch and Highway 400. It was officially opened and blessed on May 16, 2008. The new school was designed by ZAS Architects and built by Aquicon Construction and includes a three-storey building with a six-lane track and full-sized sports field. Since then, Johnson is home to over 1000 students serving northern Etobicoke and northwestern North York with ethnic groups ranging from Blacks, Filipinos, Hispanics, Poles, Croatians, Arabs and South Asians. ==Academics==