William Johnson was Private 9108 in the 8th (Service) Battalion East Yorkshire Regiment.
Born in Crawley about 1889, he was the son of James and Annie Johnson, his father being a Cowman on the Tilgate Estate. William was a Crawley resident when he enlisted in Haywards Heath and was the brother of James Johnson who was killed early in the war on 27 February 1915 in fighting around Ypres in Belgium and is also commemorated on the memorial.
William was listed as missing, assumed killed in action on 3 May 1917 in an attack on Hoppy Wood as part of the 2nd Battle of Arras.
Annie Johnson, his mother, is mentioned in this article from the Crawley Observer from 2011: