Mary Kavanagh was born at Fair Green, Arklow, on 15 August 1903, the daughter of Denis Kavanagh and Julia Reilly. Her birth was registered on 28 September 1903 by midwife Sarah Massey of Fair Green, who was present at the birth.
Listed as living in Household 11, Rock Big with her parents and seven siblings; Patrick, Lizzie, Denis, James, William, Edward and Michael.
Mary was not living in the family home at Askintinny by the time of the 1926 census.