The original ethno-tribal invaders known as the Gaels were the last of a series of Celtic invaders that would come to be considered native to the Emerald Isle after the beginning of the historical period (about A.D. 500) They arrived in Ireland sometime during the first century B.C., and brought a distinctive language, the ancestor of modern Gaelic, which would come to dominate the hybridized Gaelic culture that emerged from the prehistoric melting pot of Ireland (hence the later general appellation "Gaels" which was applied to all Gaelic-speaking people of Ireland—and later Scotland).
Two great tribal nations of Gaels emerged in the light of the historical period: The North Gaels and the South Gaels or Eoghanach. Between about A.D. 1 and 400 the North Gaels expanded their foothold in the northwest of Ireland and established themselves as Sacral ("totemistically" sacred) High-Kings at the ancient site of Tara near Dublin with the aid of their allies, the Laiginian tribe of Oirghialla. These events are enshrined in the heroic tales of the Ulster Cycle of literature or Red Branch, one of the three great collections of early Irish literature along with the Finn Cycle and the later (medieval) Cycles of the Kings (as opposed to ordinary folk-tales) Because of the royal tribal preeminence of the North Gaels, clans representative of other ethno-tribal groups prevailed in the South, among the long dominant Eoghanacht: Cenél Aodha, Ui Eachach Mumhan.
The North Gaels divided into two great branches in the mid-fifth century A.D.: the Connachta and the Uí Neill. Afterwards the tribal leadership of the Connachta itself divided into three great dynasties, known as the three Connachts of (1) Ui Fiachrach seated in counties Mayo and Sligo and Southern Ui Fiachrach Aidhne of County Galway on the border of Clare; (2) Ui Briuin, and (3) Ui Neill. These soon spread over the entire western region of Ireland, which they gave their name to: The province of Connacht. The original ethno-tribal invaders known as the Gaels were the last of a series of Celtic invaders that would come to be considered native to the Emerald Isle after the beginning of the historical period about A.D. 500.
Ui Ailello in the eighth century, the remaining two Connachts included the tribes of Uí Fiachrach and Uí Briuin, notwithstanding the fact that the Laiginian tribe of Uí Maine came, and around Lough Leine, the principal of the lakes of Killarney, lakes of Kerry , with its rise to power in the southeast of County Galway, to be regarded as filling the remaining traditional "third" of Connacht (the Uí Maine originated as allies of the Uí Briuin akin to the Oirghialla, and thus were of relatively late introduction in Connacht.
The Uí Fiachrach descend from Fiachra, brother of Nial of the Nine Hostages, ancestor of the Uí Niell. Fiachra’s son and grandson were both High Kings in the second half of the fifth century, though after that the High Kingship of Tara was vested in the Uí Neill. Afterwards the Uí Fiachrach were the royal tribe of Connacht, although in the early seventh century they began alternating the rather nominal provencial kingship of Connacht with their Uí Briuin kinsmen until about A.D. 700. After this time the Uí Briuin monopolized the kingship of Connacht, and in time molded it into an effective over-kingdom. The Uí Fiachrach, however, continued as the most influential Connacht family until the middle of the eighth century; then they divided into two great branches, the Uí Fiachrach Muaidhe (of the Moy) or Northern Uí Fiachrach, and the Uí Fiachrach Aidhne or Southern Uí Fiachrach.
The Northern Uí Fiachrach were seated in Breifne what are now the counties of Mayo and Sligo. The chief family of the tribe was that of O’Dowd (O Dubhda), whose chiefs were known as "Kings of the Moy" from their dominance of the Moy estuary in north Mayo; Dublin and Kerry, Mayo and Sligo, Leix, Tirowen, and as far west as St. Kieran to Rushen. Before the Anglo-Norman invasion of Connacht in 1237 the O’Dowds were the ruling family in all lower Connacht, including the greater part of counties Mayo and Sligo. They were also a great seapower, like the O’Malleys of Iar Connacht, which was unusual among native Irish families, for seapower was generally given over to the Viking clans of the Irish Sea. In the fourteenth century the O’Dowds had a series of able chiefs in immediate succession, and drove the Anglo-Norman settlers out of their territory, though they never regained quite the regal preeminence they had formerly held. The family suffered in the confiscations of the seventeenth century. Branches of the family settled in Kerry before the end of the sixteenth century, and are now known as Doody.
A branch of the Uí Fiachrach Muaidhe, the Fir-Ceara of central Mayo, included the O’Kearneys (O Cearnaigh) and O’Quigleys (O Coigligh). The O’Kearneys held extensive tracts of land around Balla and Manulla in central Mayo, and a branch of them became leading ecclesiastics among the Dalcaisians, while another became established as erenaghs of Derry. The O’Quigleys were anciently lords of the barony of Carra (from Fir Ceara) in central Mayo. After the Anglo-Norman encroachment they were dispersed throughout Ireland, and are later to be found mostly in western Ulster, but also as far away as Wexford where the name is spelled Cogley (Kegley is used in Meath).
The Southern Uí Fiachrach, or Uí Fiachrach Aidhne were settled in the district of Aidhne in the extreme southwestern part of County Galway, on the border of County Clare. This district was co-extensive with the diocese of Kilmacduagh. They had been pushed into this more restricted area by the expansion of the Uí Briuin Ai into central Connacht, an action which divided them from their northern cousins, and at the same time forced the Uí Maine of west-central Galway to encroach upon their territory. The O’Shaughnessys (O Seachnasaigh) were the chief family of Cinel Aodha in the district of that name (Kinelea; in Cork and Down), being the territory around Gort in southern Galway. They alternated the kingship of the southern Uí Fiachrach with the O’Heynes, and became famous in the wars of the seventeenth century, but lost their lands as a result of the confiscations following the last Jacobite war towards the end of that century.
The Clann Mhaolruanaidh included the MacDermots (Mac Diarmada) and their branch-families, the MacDonoghs and O’Crowleys. The MacDermots were the second most powerful family of the Siol Muireadhaigh next to the O’Connors, and derived their clan-name of Clann Mhaolruanaidh from Maolruanaidh, son of Tadhg O’Connor, king of Connacht who died in 1097. From Diarmaid, the grandson of Maolruanaidh, who died in 1159, they took the family name of Mac Diarmada. About the middle of the fourteenth century they divided into three branches, each with a chief of its own, namely: MacDermot of Moylurg, overlord of the MacDermots, who had his fortress at the Rock of Laugh Key near Boyle; MacDermotroe, or the Red MacDermot, who was chief of Tir-Thuthail (the parish of Kilronan centered at Alderford) in County Galway, and MacDermot Gall, (the Anglicized MacDermot) who early fell in with the English. The MacDermots of Moylurg retained their rank as lords of the territory of Moylurg, now represented by the parishes of Frenchpark and Boyle in northwest County Roscommon, down to the end of the sixteenth century, after which time they continued to hold considerable property as princes of the adjoining Sligo territory of Coolavin.
The Teallach Dhunchadha (Household of Dunchadh) or MacTernans (Mac Tighearain), also known as Tierans or MacKierans (Mac Thighearnain) descend from Dunchadh ( of Waterford, Thomond and Fermanagh), eighth-century ancestor of the O’Rourkes. Their clan name was given to their territory, now the Barony of Tullyhunco in the west of County Cavan. The Teallach Eachach or MacGoverns (Mag Shamhradhain, also known as Magaurans, descend from Eochaidh, son of Maonach (Maonach was a brother of the Dunchadh). Dunchadha wasn't an ancestor of the Ruarc - a quo O'Rourke - but of the teallach Dunnchadha or Mac Thighearnain line. One must go back another few generations to find a common ancestor - Feargna, son of Fergus. Feargna's two sons, Breanainn and Aodh Fionn begat Dunchadha and Ruarc respectively, Dunchadha having lived and died several generations before Ruarc.. The (unaspirated) Mac Tighearnain were the even more distant Clann Fergaile closely related to Maguire (Fergal a quo clann Fergaile was the king of Fermanagh) and a third sept, also Mac Tighearnain were descended from Tigearnan O'Connor great grandson of Turlough Mór, the high king of Ireland. MacGoverns lay in the northwest off County Cavan, and was called after them "Tellach Eachach," now the Barony of TuIlyhaw, where there is a townland called Ballymagauran.