| Thornhill Secondary School | |
|---|---|
 | |
| Location | |
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167 Dudley Avenue ,, L3T 2E5 Canada | |
| Coordinates | 43°48′35″N79°25′13″W / 43.80972°N 79.42028°W /43.80972; -79.42028 |
| Information | |
| School type | High school |
| Motto | Post Proelium Praemium - "After the Struggle, the Reward" |
| Religious affiliation | Secular |
| Founded | 1954 |
| School board | York Region District School Board |
| Superintendent | Donna Donalds |
| Area trustee | Jenny Chen |
| School number | 947792 |
| Principal | Karen Fogleman |
| Grades | 9-12, offers AP level subjects |
| Enrolment | 939[1] (October 2024) |
| Language | English |
| Colours | Black and Yellow |
| Mascot | Theodore The Tiger |
| Newspaper | Eye of the Tiger |
| Website | www |
| Last updated: November 2025 | |
Thornhill Secondary School (TSS) is asecondary school inMarkham,Ontario,Canada, within the namesakeThornhill neighbourhood. Founded in 1955, the school is administered by theYork Region District School Board system.
Originally it served as an elementary school, but in 1956 it opened as a full-time high school with 600 students. The TSS library was established in 1960 and renovated in 2007. In 1962, the school increased its classrooms from 30 to 47 and added 32 members to its original faculty of 29.
By 1962, 1090 students were enrolled. A technical and commercial wing was built in 1961. In 1976, the school undertook a major renovation. That same year, the drama program started and the music program expanded. In 1999, an expanded science wing was constructed to accommodate an overflow of students. A new library and school hallway connecting science to the technologies and music was completed in June 2007.