The Érainn were the second of the Celtic groups to come to Ireland, They arrived from the Continent between 500 and 100 B.C., and established their La Tène culture throughout the island as a military aristocracy possessing superior iron weapons technology. They were akin to the Belgae of Southwest Britain, and were generally known as the Ulaid in the North, and as the Érainn or Desi in the South, although all the tribes of this ethnic group were known ultimately to be Érainn.
The great Érainnian population groups of around A.D. 600, such as the Muscraige of Munster, gave rise in the Middle Ages to the independently branched tribal groups that follow. When the first inhabitants of the Arans, probably coastal fishers from the Connemara region, arrived on Inis Mór, they found it divided into two distinct regions, much as it is today. The highest parts of the island faced the Atlantic, sheltering the fertile lowlands from the violent storms that lash the western coast of Ireland. From their safe harbors facing the Connemara coast, the islanders could send out boats to catch the abundant fish of Galway Bay or the Atlantic, and they could build houses and farms on the sheltered lowlands. Irish (Gaelic) is still the first language for many of the inhabitants.
The Dal Riada were originally a tribe of North Antrim in Ireland, but from as early as the third century, and especially during the late fifth century there had been a steady settlement of the adjacent coastal and island areas of Scotland by these Dal Riada Scots. This area, which became the Scottish part of the greater tribal kingdom of Dal Riada, was separated from the rest of Scotland by mountains. The Scottish part of the tribal kingdom of Dal Riada was known as Argyll which means "coastland of the Gaels," for by this time the population of Ireland had long been Gaelic-speaking, and the Dal Riada considered themselves to be Gaels in the general sense, though nonetheless Érainn in the context of ethno-dynastic politics. About A.D. 500 the kings of Dal Riada took up permanent residence in the Argyle, and with the coming of the Vikings in the ninth century, the tribe, by then centered in Argyle, was cut off from their Irish collateral kinsmen in Antrim, the O’Quins of Antrim, who declined in power after the Anglo-Norman invasion. The chief kindreds of the Dal Riada of Argyle, the Cineal Loairn and the Cenél nGabrain, soon spread into much of Scotland with the uniting of their kingdom and the Kingdom of the Picts.
The Clann Chointeagain (or MacGilfoyles) The Clann Choinleagain or MacGilfoyles (Mac Giolla Phoil) were an ancient clan in the territory of the O’Carrolls of Ely, being chiefs of the territory around Shinrone, South Offally.
The Corca Dhuibhne were a great clan in West Kerry, the chief families of which were the O’Connells and the O’Sheas. The O’Connells (0 Conaill) of Kerry were formerly chiefs of Magh 0 gCoinchin, in the east of County Kerry until dispossessed by the O’Donoghues about the middle of the eleventh century.
The O’Connells then followed MacCarthy Mor, for whom they were hereditary castellans of Ballycarbery, near Caherciveen. The O’Sheas (0 Seaghdha) were formerly lords of the present Barony of Iveragh in West Kerry, but were somewhat displaced about the time of the Anglo-Norman invasion in the twelfth century.
The Corca Laoighdhe were a great clan in the southwest of County Cork. Their territory was coextensive with the Diocese of Ross, and their chief families were those of O’Coffey, O’Dinneen, O’Driscoll, O’Flynn, O’Hea, 0’Hen-nessy and O’Leary.
The O’Coffeys (0 Cobhthaigh) were formerly a powerful family of West Cork. They were seated in the barony of Barryroe, where Dun Uí Chobhthaigh, Dunocowhey, marks the site of their residence.
The O’Dinneens or Dennings (0 Duinnin) were a literary family, and became hereditary historians to MacCarthy Mor, chief of the MacCarthys, and also to the O’Sullivans.
The O’Driscolls (0 hEidirsceoil) were powerful chiefs in West Cork, being originally lords of the whole southwest of that county, the baronies of Carbery, Beare and Bantry. After the Anglo-Norman invasion, their territory was reduced by the encroachments of the O’Donovans, O’Mahonys and O’Sullivans, as a reaction to Norman pressure on those families. From that time the O’Driscolls possessed the seacoast area around the Bay of Baltimore, and were still a considerable power in the area in the seventeenth century, with several strong castles. They took an active part in the Munster wars during the reign of Queen Elizabeth. After the defeat of Irish forces at Kinsale, the property of the O’Driscolls was confiscated and given to Lord Castlehaven.
The O’Flynns (0 Floinn) of Ardagh were anciently chiefs of the Barony of Ibawn, in the south of County Cork. The chief of the family resided at Ardagh Castle between Skibbereen and Baltimore.
The O’Heas (0 hAodha) were sub-chiefs, under the Barrys, of Tuath 0 DonnghaiLe in the southwest of County Cork.
The O’Hennessys (0 hAonghusa) of Corca Laoighdhe were chiefs of a territory in southwest Cork near Ross Bay. A scion of this family, Richard Hennessy, was born in 1720, and followed relatives into the French Service, becoming an officer in Dillon’s regiment. He rose to high office in the French government, settled in Cognac, and married into the Martell family, afterwards founding the House of Hennessy cognac.
The O’Learys (0 Laoghaire) were originally chiefs of the territory lying around Rosscarberry in West Cork, but removed from there about the time of the Anglo-Norman invasion (twelfth century). They had a reputation as a maritime power from before the 1100s, and later became lords, under the MacCarthys, of the country between Macroom and Inchigeelagh. In 1642, sixteen leading men of the name were attainted (legally deprived of civil rights), including Connor O’Leary of Carrignacurra and Auliff O’Leary of Cunnowley. The O’Learys are now numerous throughout Munster.
The Uí Bloid were a branch of the Uí Toirdealbhaigh whose territory originally lay around the deanery of Omulled in the east of County Clare. Besides the O’Shanahans and O’Duracks, the Uí Bloid comprised the chiefly families of O’Aherne and O’Kennedy. The Uí Cearnaigh, of which the O’Ahernes (0 Eachtighearna) were the chief family, inhabited the territory around Six-mile-bridge until they were driven out about 1318 by the MacNamaras. Afterwards they are found chiefly in Limerick and Cork, but also in Waterford.
The Cenél mBaoith were one of the original Dalcassian clans from the time of Brian Boru. Their representatives in historical times were the O’Hartagans and the O’Lonergans. The O’Hartagans (hArtagain) are a Dalcassian sept of Limerick, and are descended from Dunlaing O’Hartigan, one of the heroes of the battle of Glontarf, who fought against the Vikings in 1014 under O’Brien. The O’Lonergans (0 Longargain) are a Dalcassian sept that was originally settled in County Clare in the earlier Middle Ages, but after 1318 they settled in Tipperary after being driven from their original patrimony by the O’Briens and MacNamaras. The family produced a number of great ecclesiastics during the Middle Ages.
The Clann Dealbhaoith anciently inhabited the Barony of Bunratty, in the south of County Clare. The main stem of the clan was the ancient family of Ó Neill of Thomond, but this family is now represented by its two modern branches, O’Nihills of Limerick (from the Norse form of Ó Neill) and the Creaghs of Bunratty. The Greaghs (Craobhach) derive their cognomen of Creagh from one of their ancestors who carried a green branch in a battle against the Limerick Vikings (called Danes though of Norwegian origin). They subsequently became a respectable merchant family in Limerick, and later also in Cork, while keeping up their connection with Clare as well. The family provided several distinguished churchmen in the fifteenth century.
The Muintear Ifearnain or O’Quins (0 Cuinn) descend from Conn, Lord of Muinntear Ifearnain, who flourished in the latter part of the tenth century. They were originally seated at Inchiquin, and their territory, which was designated Muinntear Ifearnain from their clan name, comprised the country around Corofin, in County Clare.
The O’Deas (0 Deaghaidh) were the chief family of the Uí Fearmaic, being the lords of the territory of that name in northwest County Clare, which comprised the greater part of the present Barony of Inchiquin. They had their chief strongholds at Tullyodea and Dyserttola; a branch where chiefs of Slewardagh in East Tipperary. The O’Griffeys (0 Griebhta) were the chief family of the Cenél Guallachta in the southeast of what is now the barony of Inchiquin (the northwest quarter of County Clare, just east of the coastal baronies of Corcomroe and the Burten). They followed the O’Deas, and had their castle at Ballygriffy in the parish of Dysert, near Ennis. The name is usually Anglicized as Griffin.
The Maclnerneys (Mac an Airchinnigh) are of the same stock as the MacNamaras, and formerly held considerable property around Ballycally, in the parish of Kilconry and Barony of Bunratty (South Clare), which they lost in the Cromwellian confiscations. The family is now numerous in Clare and Limerick. Their name denotes descent from an erenagh, or hereditary ecclesiastic.
The MacNamaras (Mac Conmara) were the chief family of the Uí Caisin or Clann Chuileain. They were, next to the O’Briens, the most powerful of the Dalcassian families, and were hereditary marshalls (military commanders) to the O’Brien kings of Thomond. It was their privilege to inaugurate the O’Brien. Their original territory was called Uí Caisin, which corresponded to the present deanery of Ogashin, including nine parishes, in the east of County Clare. In later times, however, they ruled over a greatly enlarged territory which comprised the whole of Upper and Lower Tulla, the entire eastern quarter of County Clare. This territory was known, from their other clan name, as Clann Chuileain. In the sixteenth century a branch of the family settled in County Down.
The Ulaid were the great Érainnian people who gave their name to Ulster, and they who are celebrated in the Ulster Cycle. Their direct royal representatives in historical times were the Dal bhFiatach of County Down, but they also encompassed the Uí Duach and Dal Riada as well. The Dal bhFiatach or MacDonlevys (Mac Duinnshleibhe) were a warlike clan that held great power in County Down and South Antrim until 1177, when they met and were defeated by the Norman army under John de Courcy, though only after brave resistance. The battle occurred near Downpatrick. After this defeat the MacDonlevys were reduced in power, although as late as 1273 they were referred to as kings of Ulidia (Uladh), the name of their original territory. Afterwards branches of the clan sought new homes as far away as Scotland. The main line became hereditary physicians to the O’Donnells, and had their new patrimony in Tirconnell (County Donegal). The MacDonlevys are also known as MacNultys or Ultachs (Mac an Ultaigh) , which literally means "Son of the Ulidian."The MacNallys (Mac Con Ultaigh) of the Armagh-Monaghan border, whose name means "son of the hound of Ulidia," are also of Dal bhFiatach stock.
The Déisi were an Érainnian race. The main group so called settled in Waterford and south Tipperary at a very early date as vassal-allies of the Éoganacht Gaels of Cashel, after driving out the earlier inhabitants. The chief family of these Southern Deisi was that of O’Phelan.