Mary Kavanagh was born on 25 December 1917, at Abbey Street, Arklow. She was the third child and eldest daughter of William Kavanagh and Sarah Mary Dunne. Her birth was attended by local midwife Sarah Massey of Fairgreen and officially registered on 28 December 1917.
On the night of 18 April 1926, Mary was recorded in the townland of Ballinabanoge, Co. Wicklow, with her parents and siblings; Henry, James and Elizabeth.
Mary is listed as 8 years and 4 months old, born at Abbey Street, Arklow and attending the local school.