William's father was George Edward Unwin. George married his first wife, Alice Clayton, between October and December 1877. They are known to have had one daughter, Ester (born about 1886 and, in 1901, working as a domestic servant). Alice died between April and June 1894.
George remarried within weeks, to Sarah Holder, who was several years younger. Sarah had been born in Balsham, Cambridgeshire and, at the time of the 1901 Census, was aged 34. George was 47 and was working as a labourer on the railway. William, then aged 4, was the eldest child. He had a sister, Hilda, aged 1.
William's original service number, 754, suggests he was a pre-war member of the Territorial Army and would have been mobilised when war was declared in August 1914. William would have been only 17 - too young to go overseas, but it is likely a blind eye was turned to his age. An account of the Battalion's early service is here. His Medal Index Card, at the National Archives also notes that he served with the numbers 5262 and 15092, before being allocated his final number above at the beginning of 1917. The fact that had these intervening numbers suggests that he had periods away from the Battalion, perhaps recuperating from wounds or illness.
At some point he as wounded. After treatment near to the battlefield, he was brought back to Britain but subsequently died.