The school currently caters for about 1100 students from pre-preparatory school to Year 12.
The Illawarra Grammar School was founded in 1959 through the efforts of the late Bishop Gordon Begbie and a dedicated band of 'founding parents' who firmly believed in the need for a regional Anglican School to be based in the Illawarra. On its opening day on 3 February 1959, the first Headmaster, Rev R F Bosanquet and two staff, welcomed 28 boys into a close and caring community. In 1975, the school became co-educational when it amalgamated with SCEGGS ‘Gleniffer Brae’.
In 2009 TIGS celebrates the Golden Jubilee of its founding.
Robert Hurley of the Australian swimming team, attended the school.