Twenty acres (8 ha) at Prospect Hill were purchased from the Earl of Hertford.
The latest addition to the school is the East Suite, a teaching building containing Maths and Music classes, which was opened in 2016.
It stands in place of the old basketball court, which was previously the location of the swimming pool.
A sports hall was opened in 2000 and two floodlit, sand-dressed hockey pitches were laid in 2013.
As well as hosting school fixtures, these pitches are home to South Antrim Hockey Club.