Mountjoy Square is a garden square in Dublin, Ireland, on the Northside of the city just under a kilometre from the River Liffey. One of five Georgian squares in Dublin, it was planned and developed in the late 18th century by Luke Gardiner, 1st Viscount Mountjoy. It is surrounded on all sides by terraced, red-brick Georgian houses. Construction of the houses began piecemeal in 1792 and the final property was completed in 1818.

A garden square is a type of communal garden in an urban area wholly or substantially surrounded by buildings; commonly, it continues to be applied to public and private parks formed after such a garden becomes accessible to the public at large. The archetypal garden square is surrounded by tall terraced houses and other types of townhouse. Because it is designed for the amenity of surrounding residents, it is subtly distinguished from a town square designed to be a public gathering place: due to its inherent private history, it may have a pattern of dedicated footpaths and tends to have considerably more plants than hard surfaces or large monuments.