The Erdini, or Ernaigh according to some authorities, were the inhabitants of this district of Fermanagh with Leitrim, Cavan or Breifne in the time of Ptolemy and traces of which name are yet preserved in that of Loug Erne and the river Erne, upon which and their tributaries these discricts border. There, the Cenél Enda (Énna or Eanna) Located in the southern Co. Donegal and northern Fermanagh region. But Whitaker considers it to have been part of the Nagnatae of Co. Mayo, of its southern extremity, into which the Auterii, who were settled in the northwest of Co. Galway. For Co. Monaghan and Tyrone counties was inhabited in the time of Ptolemy by the Scoti, who then possessed all the inland parts of Ireland. The ancient kingdom of Airgialla (Oriel) was formed around AD 330. The Book of Ballymote cites a Cenél Tigearnaigh as the race of Tigearnach, son of Eoghan, son of Niall. The formation of this part of Ireland (Ciannacht or Clann Cian) into separate dominion is said to have taken place so early as the yeare 332, after the battle of Achaighleth-derg, in Fermoy, in which, as recorded by Tigernach, abbot of Clonmacnois. Conall Gulban was the son of Niall who established his kingdom, among other places, in Mag Ithe in the valley of the Finn.
Magnus Maximus, raised the standard of revolt in Segontium in 383 and fought a campaign against the Picts and Scots around 384. Forts at Chester and elsewhere were abandoned at this period, triggering raids and Danelaw settlement in north Wales (Gwynedd) by the Irish. Since the Battle of Adrianople in 378 there were increasing barbarian incursions in Britain and by 401 more troops were withdrawn to assist in the war against Alaric I, king of the Visigoths. By 409 the Roman hold on Britain was slipping away, and Britons were told to defend themselves. About this time the Celtic Gaelic tribe of Scots begins settling in the southwest of Scotland, creating the Moravian and Mormaer kingdom of Dalriada in Argyll (Oir Ghaedhil or Eastern Gaels). The Irish tribe Dal Riata hailed from the Antrim coast and part of the province of Ulster. They crossed the narrow Irish sea in their hide boats (curraghs) and mounted raids among the Attecotti and into Roman Britain.
The Érainn tribal or group name Lughaidh Laidhe (Loígde) was applied to that part of southwest Co. Cork (Desmond) and Coleraine embraced by the diocese of Ross (formed in the 12th century).
The name Dairfhinne, aka Fir Érainn, was applied to a a powerful people in Munster in the 2nd, 3rd, and 4th centuries, not considered to be of Milesian descent; Oilill Olum. 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, O’Hen-nessy and O’Leary. It included the baronies of Carbery, Beare and Bantry. It at one time extended from Beann Finn westward to Tragumina and Lough Ine and from Beal Atha Buidhe to Tragh Claen. The Feara Li, or Fer Li, i.e. the men of Mag Lí, was located west of the River Bann in the barony of Coleraine, Co. Derry. Their neighbors appear to have been the Uí Tuirtre and factions of both groups are said to have been driven to the east of the Bann (into Ulidia) by the advance of Ua Cathain of the Cenél Éoghain. The sept of Ó Floinn (e.g. O'Lynn) became kings of Uí Thuirtre and Fir Lí by the late 12th century, and the territory name, Loch Inse Uí Fhloinn, is remembered in the name of the barony of Loughinsholin, in southwest county Derry. Remembered in the barony of Dartree in west co. Monaghan, it was also referred to as Dartaige Coininnsi. The O'Boylan (Ó Baoighealláin) sept are cited as early kings of Darty (Dairtre) in Monaghan, Orghialla, during early medieval times, as lords of Airgialla, stretched from Fermanagh to Louth to Breifne.
Prior to the Reformation, the counties were in the diocese of Ross; they are at present mostly in the synod of Ross, and comprise several presbyteries, and thirty-one parishes. For civil purposes they are under the superintendence of three sheriffs-substitute, of whom one holds his courts at Cromarty and Tain, and another at Dingwall and Fortrose, and the third at Stornoway, in the island of Lewis. They contain the royal burghs of Dingwall, Tain, and Fortrose; the market-town of Cromarty, which is a burgh of barony; and numerous smaller towns and villages. Under the act of the 2nd of William IV. they return one member to the imperial parliament, the election taking place at Dingwall or Danelaw.