| St. Mary Catholic High School | |
| Address: | 40 Central Avenue |
| Country: | Canada |
| Type: | "Catholic" |
| Founded: | 1951 |
| Superintendent: | Brent Bovaird |
| Principal: | Laura Mackler |
| Chaplain: | Sean Shallow |
| Grades: | 7-12 |
| Enrollment: | 595 (2019-2020) |
| Area: | Brockville |
| Colours: | Blue and White |
| Team Name: | St. Mary's Crusaders |
| Feeders: | St. John Bosco Catholic School, J.L. Jordon Catholic School, St. Francis Xavier Catholic School, St. Joseph Toledo |
St. Mary Catholic High School Brockville is a Catholic high school in Brockville, Ontario. The school's current principal is Laura Mackler, with Stephanie Koekkoek as the vice-principal. The school has a gymnasium, library, large guidance and special education departments, five science classrooms, four English classrooms, a construction lab, music room and a stage/drama room. St. Mary also features a "cafitorium" (auditorium that is transformed into a cafeteria). The school day commences at 8:05 am and concludes at 2:08 pm. Unlike the local public schools, St. Mary only has four periods per day.
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