|Motto||Adveniat Regnum Tuum|
|Specialism||Mathematics & Physics|
|Local authority||Western Education and Library Board|
Thornhill College (Irish: Coláiste Thornhill) is a Roman Catholic girls' grammar school in Derry, Northern Ireland. It was founded by the Sisters of Mercy in 1886 and moved to Culmore in 1932. It moved into its new building in 2003. It has a student population of approximately 1500 and a staff of 100 teachers. Miss Hamilton replaced Mrs. Kelly in 2010 as the school principal.
Catherine McAuley said: "Let us rejoice when good is done, no matter by whom it is accomplished". The school strives in the words McAuley, founder of the Sisters of Mercy, "to fit young women for Earth without unfitting them for Heaven". 
The school motto is the Latin phrase "Adveniat Regnum Tuum", which translates as "Thy Kingdom come".
Thornhill College is an all-girls Roman Catholic College.
In 2009 Thornhill College became a Specialist School in Mathematics and Physics. 
The Specialist Schools Programme helps schools, in partnership with private sector sponsors and supported by additional Government funding, to establish distinctive identities through their chosen specialisms and achieve their targets to raise standards.
Notable former pupils
- Dana Rosemary Scallon - singer and former MEP,
- Nadine Coyle - member of girlband Girls Aloud
- Roma Downey - actress
- Nell McCafferty - journalist, writer and playwright
Thornhill College has a Senior Debating Society, established in 1954. The team reached final of the Northern Ireland Schools Debating Competition in 2004 and 2007, and is known throughout the school for wearing the gold stripe around the lapel of the debating blazer. Thornhill has had two teams in the semi-finals of this competition who debated against each other on 30 March 2007 in Belfast. The society meets regularly to debate topical subjects and research up and coming competitions. The school also has an established Junior Debating Society who meet after school as part of the homework club.
The school has recently erected a statue on the "teardrop" at the front of the school. The piece was constructed by Maurice Harron and the final sculpture was officially unveiled early Autumn 2008.
Thornhill College is a Grammar school with a high academic record. The college was placed 17th in the 2012 Northern Ireland league tables with 83% of its pupils passing at least three A levels.  90% of A level students in 2013 achieved 3 A*-C grades at A level or equivalent, whilst over 80 students in the same year achieved 7 or more A*/A grades at GCSE level. 
- Margery Jackman Catherine's Response, All Hallows School, 1996, Retrieved 2012-07-31
- Education Minister announces nine new specialist schools Northern Ireland Executive, 4 June 2008, Retrieved 2012-07-31
- Northern Ireland schools league tables Belfast Telegraph, 7 March 2012, Retrieved 2012-07-31
- A-Level results, Thornhill College Aug 2013
- GCSE results, Thornhill College Aug 2013