Prior to the opening of Thornhill Secondary School (originally known as Thornhill High School) in 1954, students had to commute to either Richmond Hill High School or in later years, Earl Haig Collegiate. The growing population in the post-war years put increased pressure on the existing high schools.
The impetus came in 1952, when a group of Thornhill ratepayers made an appeal to the Richmond Hill District High School Board to establish a high school in Thornhill. Thornhill High School first opened as a part-time school with 410 students. In 1956, it became a full-time high school with 600 students.
The official opening of the school was held on February 1st 1957 with great ceremony. In 1961, following extensive additions to the building, Thornhill High became Thornhill Secondary offering technical as well as academic courses.
Over the years T.S.S has continued to grow to meet the needs of its students, with the addition of the Elson Memorial Library in the 1970's, and the new science wing in 1999.
Come, let's all sing for Thornhill
Come, let's all shout for Thornhill
Thornhill, our alma mater that we revere,
We will her honour cherish,
Long may her banners flourish,
Hail to out alma mater, Hail to Thornhill.
Black, white and yellow bold,
Are the colours we uphold,
Them will we wear with pride and loyalty.
She is the school we're out for
She is the school we'll shout for,
God bless our alma mater,
God bless Thornhill.