From Irish Names and Surnames 1923
Ó DOMHNAILL—I—O Donill, O Daniell, O'Donnell, Donnell, Daniel; 'descendant of Domhnall' (world-mighty, an ancient and very common Irish personal name, now generally anglicised Daniel); the name of several distinct families in Ireland, of which the following were the most important:—(1) Ó Domhnaill of Tirconaill. This family is descended from Conall Gulban, son of Niall of the Nine Hostages, and for four centuries was one of the most powerful in Ireland. The original patrimony of this family was Cinel Luighdheach, a mountainous district between the Swilly and the Dobhar, but on the decline of the O'Muldorys and O'Canannains, some time after the Anglo-Norman invasion, they became the ruling family in Tirconnell. Previous to that event, only two of the immediate ancestors of the O'Donnells had been lords of Tirconnell, namely, Dalach, who died in 868 and from whom they derived their later clan-name of Clann Dalaigh, and his son, Eigheachan, who was the father of Domhnall from whom they took the surname of Ó Domhnaill, or O'Donnell. The family produced many able chieftains who, during the four stormy centuries that the O'Donnells held sway in Tyrconnell, not only defended their territory against foreign and native foes, but made their power respected throughout the north and west of Ireland. The most celebrated of all the chieftains of Tirconnell was Red Hugh O'Donnell, who so often led his clan to victory in the closing years of the reign of Elizabeth. Many of the O'Donnells were distinguished military commanders in the service of continental powers, and in the last century, Leopold O'Donnell became prime minister of Spain and Duke of Tetuan. The O'Donnells of Limerick and Tipperary are, according to O'Donovan, descended from Shane Luirg, son of Turlough O'Donnell of the Wine, lord of Tirconnell at the beginning of the 15th century. (2) Ó Domhnaill of Corcabaskin, in West Clare. This family derives its descent from Domhnall, son of Diarmaid, lord of Corcabaskin, who was slain at the battle of Clontarf in 1014. The O'Donnells continued to be lords of Corcabaskin until dispossessed by the MacMahons early in the 14th century. They are, no doubt, still numerous in Thomond. (3) Ó Domhnaill of Ui Maine, who were chiefs of Clann Flaitheamhail, in the present Co. Galway. (4) Ó Domhnaill of Carlow, anciently lords of Ui Drona, now the barony of Idrone. (5) Ó Domhnaill, of Cinel Binnigh, a sept of the Cinel Eoghain. (6) Ó Domhnaill of Ui Eathach, a sept of the Oirghialla, who were seated in the present Co. Armagh. The O'Donnells are now very numerous, especially in Ulster and Munster.
This group is yDNA orientated and the current project administrator does not do any genealogy work for the members.
Volunteers co-admin(s) is(are) needed that are willing to help members with their O'Donnell Genealogy and research.