St Killian's College (Irish: Coláiste Naomh Cillian, also known colloquially as Garron Tower) is a secondary school located in the Glens of Antrim area of Northern Ireland. The eponymous tower was built circa 1850 as a summer residence for Frances, Marchioness of Londonderry. The college for educating Catholic boys was founded in 1951, while the current incarnation of the school, resulting from the amalgamation of nearby colleges, emerged in 2010 after a series of reforms by the Council for Catholic Maintained Schools (CCMS).

The school is regularly listed as one of the top performing schools in Northern Ireland and ranked 5th in the A-Level table in the 2019 year.

Historically a grammar school, the school became an all-abilities school in 2010 and was renamed as St Killian's College after the CCMS announced it would be focusing on transforming every school to all-abilities.

The college's building history predates the school by over 100 years. Garron Tower was built in 1850 at a cost of £4,000 as a summer residence for Frances, Marchioness of Londonderry (1800-1865), the wealthy wife of the 3rd Marquess of Londonderry. She had inherited this part of the Antrim family's estates from her mother, Anne Katherine MacDonnell, Countess of Antrim, who married Sir Henry Vane-Tempest of County Durham.

The college was founded as St MacNissi's College, Garron Tower, in 1951 as a boarding school for boys. The buildings were acquired a year earlier in 1950 by Bishop Daniel Mageean for use as a boarding school for boys. The school opened in September 1951.

In 2005, the Council for Catholic Maintained Schools (CCMS) initiated a plan to amalgamate St MacNissi's College with two other schools, St Comgall's College and St Aloysius's High School, both located in the Antrim Coast Road area. As part of this amalgamation the college was renamed St Killian's and became an all-ability school.

The college grounds are situated on a plateau approximately 200 feet (61 m) above the Antrim Coast Road (part of the A2) at Garron Point, overlooking the North Channel and out towards the Mull of Kintyre, Scotland.

The grounds include a golf course, several sports pitches, a wooded forest, several gardens and a seawall.

The college's main building contains the priests' dining-room, priests' sitting-room, 100 desk study-hall, kitchens, cloakrooms, first-aid room, classrooms, offices, and a food-storage area.

A chapel was built in 1955 and a 150-room boarding department (now empty) was opened in 1956. A set of stables, subsequently converted to dormitories, now house music, languages and business studies classrooms.

A block used for IT, home economics, art and science is situated on the site of the old tennis courts. There is also a small golf course. At the north end, there are four sports pitches and a set of hand-ball alleys. Behind the squash courts, there is an outdoor basketball court.

The seaward wall of the school has seven cannons facing the sea which are of naval origin from the Napoleonic wars.

Towards the northern end of the sea-wall, there was a gate, lending access to a twisting path down to the Coast Road but the end of this path, where it met the Coast Road, was out-of-bounds. Just across the road and about 50 yards to the north, the Garron Point Post Office was located and the journey between the gate at the Coast Road and the post office was fraught with danger. About 400 yards north of the post office, at the bottom of Dunmaul Hill, is a "water driven" pump house where - in March 1956 - a boarder at the college died.

The school curriculum covers: Key Stage 3 (Years 8, 9 and 10) - located in the main school building, Key Stage 4 (Years 11 and 12) and Sixth Form (Years 13 and 14).

In 2018, 69% of its entrants achieved five or more GCSEs at grades A* to C, including the core subjects English and Maths.

In 2019 the school was ranked 5th out of 159 secondary schools in Northern Ireland with 92.0% of its A-level students who entered the exams in 2017/18 being awarded three A*-C grades.

• Danny Donnelly - Alliance Party Member of the Legislative Assembly (MLA)
• Patricia O'Lynn (born 1990) - academic and Alliance Party Member of the Legislative Assembly (MLA)

• Official school website