Sidney Milton Day was born 24 August 1887 in Cooma, New South Wales, Australia to Thomas Day (1859-1922) and Elizabeth Jane Norris (1869-1962) and died 15 April 1960 Cooma, New South Wales, Australia of unspecified causes. He married Ethel Caroline Lila Scrutton (-c1963) 17 October 1916 in St. Mary's Roman Catholic Cathedral, Sydney, New South Wales, Australia.
Children
| Name | Birth | Death | Joined with |
| Clarence Milton Day (1921-1982) | |||
| Aubrey Anthony Richard Day (1924-2005) | May 1924 Redhaven Private Hospital, North Sydney, New South Wales, Australia | 6 October 2005 New South Wales, Australia | Joan Francis Spies (bef1945-) |