St. Mary's College is a former high school and junior seminary that was operated by the Congregation of the Most Holy Redeemer, a missionary order of the Roman Catholic Church more commonly known as "Redemptorists." The school was located on a campus on the north bank of the St. Lawrence River in Maitland, Ontario, several kilometres east of Brockville. St. Mary's College was the First Novitiate for Chorists and Laybrothers from 1944-1947 and it reopened as a juvenate in 1947 and operated as such until its last class graduated in June 1968.