St Mary’s Hospital was built in 1769 and was originally the Royal Hibernian Military School. The building was subsequently developed as a hospital by the Irish Army and in 1948 the hospital was transferred to the Dublin Health Authority and developed as a Chest Hospital. In 1964 the hospital became a facility for older people.
St Mary’s Hospital primarily provides accommodation to dependent older persons. The designated centre within St Mary’s Hospital comprises a number of wards. Teach Iosa and Teach Chara are is modern purpose-built facility that opened in 2008 and 2009, in Teach Iosa, there is also a coffee shop in the foyer which allows residents, staff and visitors to meet socially. Recreational opportunities are provided to residents in Deer Park Lodge.