The nucleus of the present Thornhill College commenced shortly after the Sisters of Mercy came to Derry in 1848.

After many years of much effort, the present building was approved and opened in 2002 across the road from the old site in the new Thornhill College.

[3] The school motto is the Latin phrase "Adveniat Regnum Tuum", which translates as "Thy Kingdom come".

[4] In 2018, Thornhill College was ranked 17th out of 192 schools in Northern Ireland in terms of its A-level performance.

[8] The society meets regularly to debate topical subjects and research up and coming competitions.