Just a short walk from the Phoenix Park, St. Declan’s was founded by the Christian Brothers in 1960. The first Principal was Br. Tommy O’Dowd. The first lay Principal, Mr. Jack Cleary, was appointed in 1991.
From an initial intake of 120 students, the school has grown to its present size of 650. To cater for this expansion, a major new extension was built between 1978 and 1980, comprising a gymnasium, a library, science laboratories, an art room, workshops for woodwork and metalwork, a large cafeteria, general classrooms and an oratory.
A further extension in 2000 added a modern computer facility, nine new classrooms and changing rooms. An intranet connecting all rooms in the school was installed at this time. With its extensive flower-beds and lawns, the campus provides an aesthetically pleasing environment for learning, with the most up to date equipment available in all classes.