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]
History
According to historian C. Thomas Cairney, the O'Tooles were one of the chiefly families of the Uí Dúnlainge who in turn were a tribe from the Dumnonii or Laigin who were the third wave of Celts to settle in Ireland during the first century BC.[4] The O'Tooles as descendants of the Kings of Leinster is supported by John O'Hart in his 1892 Irish Pedigrees; or, The Origin and Stem of The Irish Nation. O'Hart also states that the O'Tooles were chiefs of the Hy-Muireadaigh,[5] also known as the Uí Muiredaig who were a branch of the Uí Dúnlainge.
The first to use the surname in true hereditary fashion appears to have been the grandson of Tuathal Mac Augaire, Doncaon, slain at Leighlin in 1014.[citation needed]
Despite the proximity of Dublin, the centre of English rule in Ireland, the Ó Tuathail's maintained a fierce independence, and were a source of great fear to the inhabitants of Dublin and the Pale for almost four centuries. With their kinsmen the O'Byrne family, they were noted for their tough resistance to English domination, including exercising great influence over the foundation of the Confederation of Kilkenny in 1642 in what had become Confederate Ireland.
At the start of the 16th century, there were five great houses, all, owing allegiance to "The O'Toole of Powerscourt" as the recognized chief:[6]
O'Toole of Omey, Iar Connaught, with other minor houses of the family such as OToole of Ballineddan and Brittas, in the Glen Imaile; O'Toole of Toolestown, near Dunlavin; O'Toole of Glengap, or Glen of the Downs (as it is now called); and a few others.
At the start of the 16th century, the leading branches of the clan were to a certain extent independent of each other; they were all bound to protect themselves; but in external matters affecting the whole clan they were bound to obey the head of the sept.[8]
Throughout their history the family were famous as soldiers, from fighting the English in the glens of Wicklow to serving in the armies of other Catholic European countries in the 18th century, such as France and Spain.[citation needed]
The descendants of the sept took the name O'Toole or Toole, although the name is now rare without the prefix 'O'. The tradition of surnames in Ireland developed spontaneously, as the population increased and the former practice, first of single names and then of ephemeral patronymics or agnomina of the nickname type proved insufficiently definitive. At first the surname was formed by prefixing 'Mac' to the father's Christian name or 'Ó 'to that of a grandfather or earlier ancestor.
Names that are related to Ó Tuathail include: O'Toole, O'Tool, Toole, Tooles, Tool, Toil, Tooley, Toal, Toale, Tohill, Toohill, Towle, Towell, Tollan, Tolan, Toland, Tooill, Toop, Toolan, Toulan.[citation needed]
This article incorporates text from this source, which is in the public domain: "History of the Clan O'Tool and other Leinster Septs" by Patrick Laurance O'Toole