The O'Toole (Irish: Ó Tuathail) family of County Wicklow, formerly one of the leading clans of Leinster, descended from Tuathal mac Augaire, King of Leinster (died 958), of the Uí Muiredaig branch of the Uí Dúnlainge dynasty.
Not all people with this surname are necessarily related to this specific family, there being several other Irish families of the name.[1][2][3]