John McIlroy was born at 44 Colin Street in Belfast, Ireland on 13 February 1890¹. Hailing from a Roman Catholic family, he was the son of Patrick McIlroy, a flax dresser, and he former Jane Kerr. 

He had three younger sisters, Mary Ellen (b. May 1891), Jane (b. October 1893) and Margaret (b. August 1896). 

The year 1897 was a tragic one for young John: firstly, on 12 January his youngest sibling Margaret died from malnourishment aged just five months; his mother, ill with tuberculosis, died only weeks later aged 26 on 29 January. His sister Jane, always a poorly child, died in March 1897 from a lung disorder.

His father, a young widower, remarried in October 1899 to widow Mary Jane Feeney, née Hughes, a native of Co Tyrone; through that relationship he had a half-sister, Elizabeth (b. July 1902). By 1911 the family lived at 10 Varna Street off the Falls Road in west Belfast but John was not listed and was presumably at sea at the time. 

In April 1912 McIlroy was serving as a seaman aboard the eastward-bound voyage of the Carpathia when that ship rescued the survivors of the Titanic. 

Although McIlroy is known to have continued working at sea, his final whereabouts remain unclear. There is some indication that he remained in Britain and possibly died in Wallasey in the early 1960s.