Thornhill Secondary School
| Thornhill Secondary School | |
|---|---|
| Location | |
167 Dudley Avenue , , L3T 2E5 Canada | |
| Coordinates | 43°48′35″N 79°25′13″W / 43.80972°N 79.42028°W |
| 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 (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 a secondary school in Markham, Ontario, Canada, within the namesake Thornhill neighbourhood. Founded in 1955, the school is administered by the York Region District School Board system.