William Johnston was the youngest son of Thomas and Barbara Johnston. He was born about 1894. He was one of eleven children. Most of the family were born in the Enniskillen area. By 1901 the family were living in Castlecaulfield. They later moved to Belfast. William was a grocerís assistant. Private William Johnston was serving with the 9th Battalion of the Royal Irish Rifles when he was killed in action on the first day of the Battle of the Somme on Saturday 1st July 1916.
The Thiepval Memorial will be found on the D73, next to the village of Thiepval, off the main Bapaume to Albert road (D929). Each year a major ceremony is held at the memorial on 1 July. The Thiepval Memorial to the Missing of the Somme is a war memorial to 72,337 missing British and South African servicemen who died in the Battles of the Somme of the First World War between 1915 and 1918, with no known grave. It is near the village of Thiepval, Picardy in France. Designed by Sir Edwin Lutyens, Thiepval has been described as "the greatest executed British work of monumental architecture of the twentieth century"