Joseph O’Reilly was born in Limerick on 15 April 1893 and baptised in the Church of St. Michael Parish. At this time the family lived in Henry St., Limerick. His parents were Patrick O’Reilly, a Clerk, and Margaret (nee Noonan) who married on 5th June 1892 in St. Michael’s Church, Limerick. He had one sister Margaret O’Reilly who was born on 27 April 1894 and at this time the family lived at 31 Patrick St. When baby Margaret was just six weeks old, their father, Patrick O’Reilly aged 24, died of “Traumatic Gangrene,” in Barringtons Hospital, Limerick on 7 June 1894.
A few years later, their mother, a widow, married Edward Howard in Limerick on 15 January 1898. They had two Howard children and were living in Windmill St Limerick according to the 1901 Census. On that Census night Edward was working as a fireman on a ship laying off Hauley’s Quay, Limerick.
However, in Census 1911 the family, Edward Howard (Engineer on a steam vessel), Margaret Howard (his wife), and children Patrick Howard, Thomas Howard, Joseph O’Reilly and Margaret O’Reilly were in Chapel Street, Bantry. In this Census report (1911), Joseph O’Reilly is 18 years old, and is recorded as working as a Wool Weaver.
Apparently, Joseph O’Reilly went to London later in 1911, where he met Michael Collins (who was later ambushed at Béal na Bláth) through GAA and other Irish social circles.