Family History and Genealogy Resources by Surname
O'Neil Surname Origin
The descendants of Neil, that is, the powerful or mighty.
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.
O'Neil Surname Meaning and Family Facts
There is more to O'Neil family history than the origin of your surname:
A O'Neil Family History Thought:
'There is no king who has not had a slave among his ancestors, and no slave who has not had a king among his.' --Helen Keller