 Collins was born in Woodfield, Sam's Cross, near Clonakilty, County Cork, on 16 October 1890, the third son and youngest of eight children.His father, Michael John (1816–1897), was a farmer and amateur mathematician, who had been a member of the Irish Republican Brotherhood (IRB) movement.The elder Collins was 60 years old when he married Mary Anne O'Brien, then 23, in 1876.