Donegal
In the time of Ptolemy it was inhabited by the Vennicnii and the Rhobogdii, the latter of whom also occupied part of the county of Londonderry. The Promontorium Vennicnium of this geographer appears to have been Ram's Head or Horn Head, near Dunfanaghy; and the Promontorium Rhobogdium, Malin Head, the most northern point of the peninsula of Innisoen or Ennishowen, The county afterwards formed the northern part of the district of Eircael or Eargal, which extended into the county of Fermanagh, and was known for several centuries as the country of the ancient and powerful sept of the O'Donells, descended, according to the Irish writers, from Conall Golban, son of Neil of the Nine Hostages, monarch of Ireland, who granted to his son the region now forming the county of Donegal. Hence it acquired the name of Tyr-Conall, modernised into Tyrconnel or Tirconnel, "the land of Conall," which it retained till the reign of Jas. I. The family was afterwards called Kinel Conall, or the descendants or tribe of Conall. Fergus Ceanfadda, the son of the founder, had a numerous progeny, among whom were Sedna, ancestor of the O'Donells, and Felin, father of St. Cohunt. Cinfaeladh, fourth in descent from Ceanfadda, had three sons, one of whom was Muldoon, the more immediate ancestor of the O'Donells, and another, Fiamhan, from whom the O'Dohertys, lords of Innisoen, derive their descent. A second Cinfaeladh, eighth in descent from Fergus Ceanfadda, was father of Dalaga, from whom the O'Donells are sometimes styled by the Irish annalists Siol na Dallagh, the sept of Daly, or the O'Dalys. Enoghaine, his eldest son, was father of Donell, from whom the ruling family took the surname it has borne ever since. His great grandson, Cathban, chief of the sept in the reign of Brian Boroimhe, first assumed the name of O'Donell as chief, which was adopted by all his subjects and followers. Besides the O'Dohertys, the septs of O'Boyle, Mac Sweeney, and several others were subordinate to the O'Donells of Tyrconnel.
The chieftaincy of Nial Garbh, who succeeded his father Turlogh an Fhiona in 1422, was the commencement of a sanguinary era of internal diseord aggravated by external warfare. This chieftain, after having endured much opposition from his brother Neachtan, and maintained continual hostilities with the English, by whom he was at length taken prisoner, died in captivity.
The first effort of importance made by the English to subjugate this territory commenced by their seizure of the convent of Donegal and a castle of the O'Boyles, giving them a temporary command over the adjacent territory, from all which they were quickly expelled by the celebrated Hugh Roe, or Red Hugh, O'Donell, who succeeded to the chieftaincy in 1592. This powerful toparch, at an early period of his government, marched into Tir Owen against Tirlogh Luineagh O'Neil, chief of the sept of the same name and a partizan of the English, whom O'Donell, although he had recently entered into terms of amity with the Lord-Justice of Ireland, expelled from his principality in 1593, forced him to resign the title of O'Neil in favour of Hugh, Earl of Tyrone, and afterwards compelled the whole province of Ulster to acknowledge his superiority and pay him tribute. He then sent an embassy to the king of Spain to aid him in the total expulsion of the English, and having obtained a reinforcement of mercenaries from Scotland, carried on a successful war far beyond the limits of his own territory.
Transcribed from A Topographical Dictionary of Ireland, 1840 by Samuel Lewis