The Bishop Allen Academy site is situated on 14+1⁄2 acres on a ravine that runs parallel to the Mimico Creek.

The house was eventually demolished in 1961 and the Etobicoke Board of Education constructed Kingsmill Secondary School (named after the Old 'King's' Mill) in 1962 designed by the architectural firm of Gordon S. Adamson & Associates on the 721 Royal York Road building just south of Royal York Collegiate Institute (now used today as Etobicoke School of the Arts).

The exterior courtyard was enclosed with a roof to expand the existing ground floor cafeteria and a new chapel was designed by the architect Scott Morris.

[citation needed] Many immigrant families arrived in Toronto during the post-war years including many Eastern Europeans, especially Byzantine Catholic Ukrainians, whose descendants form a large part of the student body at Bishop Allen.

In 2008, health concerns about portables that contained mould forced Grade 10 students to relocate to the former St. Peter (now Monsignor Fraser College Annex) for one semester.

[7] Originally using a blue and grey colouring scheme to match the outside of the building and as a contrast to the red and black of local high school Father John Redmond, the school now has a red and black colouring scheme.

It has 28 classrooms, four science labs, an expanded cafetorium formerly used by a quadrangle, a double gym that can be partitioned, three art rooms, a library, a guidance/administrative area, and a chapel.