Family History and Genealogy Resources by Surname
O'Toole Surname Origin
Originally O'Tuathal--the descendants of Tuathal, which signifies 'the lordly.'
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'Toole Surname Meaning and Family Facts
There is more to O'Toole family history than the origin of your surname:
A O'Toole Family History Thought:
'Every man is his own ancestor, and every man his own heir. He devises his own future, and he inherits his own past.' -- H. F. Hedge