It is located on Royal York Road (formerly Church Street) at Stanley, in the Mimico neighbourhood, part of Etobicoke.

[2] In 1909 St. Leo's became a parish serving Swansea south of the College St extension (now Morningside Ave) and Mimico with its original boundaries: Lake Ontario, the Humber River, North Queen St (now Delroy Dr) and Mimico Ave (now Kipling Ave).

In 1920 the former western portion of Mimico became the Town of New Toronto, leading in 1924 to the building of St. Teresa's Catholic Church and the separation of this area from St. Leo's.

A new church was built across the street from the old at 277 Royal York Road in 1953 on the site of Mimico's 1858 post office.

In 1955 St. Mark's Catholic Church was built in Humber Bay neighbourhood and in 1961 Holy Angels was built for The Queensway neighbourhood, the area having been cut off from Mimico by the building of the Queen Elizabeth Way.