Family History and Genealogy Resources by Surname
William Surname Origin
From the Belgic Guild-helm, harnessed with a gilded helmet; or, as others say, from Welhelm, the shield or defense of many.
Source: An Etymological Dictionary of Family and Christian Names With an Essay on their Derivation and Import; Arthur, William, M.A.; New York, NY: Sheldon, Blake, Bleeker & CO., 1857.
William Surname Meaning and Family Facts
There is more to William family history than the origin of your surname:
A William Family History Thought:
What is past is prologue.