In the time of Ptolemy it was inhabited by the Scoti, which tribe extended itself over most of the inland regions; though some writers place the Erdini here, as well as in the neighbouring maritime county of Donegal. It was afterwards known as the district or kingdom of Cineal Eoghain, frequently called Tyr-Oen, whence its present name of Tyrone is derived: a portion of its southern border embraces the northern parts of the ancient district of Orgial or Uriel. According to Camden it was divided into Upper and Lower, or North and South Tyrone by the Slieve Gallion mountain; but as this range is now wholly included within Londonderry, it is probable that the name of Tyrone was then extended to the greater part of that county also. This district was from the earliest period of the Irish annals the chief seat of the power of the O'Nials, the princes or kings of the country, who traced their origin from Nial of the nine hostages, and several of whom obtained the sovereignty over the whole island. In the tenth century, Hugh O'Nial, lord or chief of Tyr-Oen, was solicited by Malachy, King of Ireland, to assist him against Brian Boroimhe, then claiming the rank of King of Ireland, and was offered a large portion of Meath as the reward of his acquiescence. O'Nial of Tyrone was one of the chiefs in Roderic O'Conor's army in his unsuccessful attempt to drive the English out of Dublin, In 1177, his death is recorded under the title of King of Tyrone. On the second arrival of King John in Ireland, O'Nial, who had been a formidable opponent to De Courcy during his invasion of Ulster, was prevailed on-to give his personal attendance on the king, but not until two hostages had been sent for the security of his person, Hen. III., in a letter to the Irish subordinate princes who had done homage to the English sovereign, styles him O'Ne'l regi de Kinelum sive Tir-Oen, The O'Nial family was also one of the five Irish septs which were specially entitled to the enjoyment of English rights and privileges. On the first arrival of Rich. II, in Ireland, O'Nial met him in Drogheda, being the first of four native princes who waited on that king. During this period and for many years after, this territory, of which Tyrone was the principal part and the usual seat of the ruling prince's residence, was untouched by the English; while, on the contrary, their borders were exposed to his predatory incursions, O'Nial was one of the adherents of Edward Bruce in his attempt to conquer Ireland. In 1333, on the death of the Earl of Ulster, who was assassinated at Carrickfergus by his own servants, O'Nial crossed the Bann and seized part of the counties of Down and Antrim, which he parcelled out into the districts of the Upper and Lower Claneboy, and these continued subject to the family till the reign of Jas. I. In the reign of Hen, VIII., Hugh Baccagh, or the Lame, invaded Meath, but was afterwards induced to submit to that monarch, by whom he was honoured with a collar of gold; and though he had supported the Kildare family during its rebellion, he was not only pardoned but had the title of Earl of Tyrone conferred on him, with remainder to his illegitimate son Matthew. On his death, however, his legitimate son John, better known by the name of Shane O'Nial, assumed the family title and seized on the inheritance, claiming the sovereignty of the province, and arrogating the supremacy over all the subordinate clans; after maintaining a desultory warfare against the English government, he was assassinated by Alexander Oge McConnell, or McDonnell, the leader of the Scots in Ulster, to whom he had recourse for protection when unable to give effectual resistance to the English. The title was claimed after his death by Tirlogh Leinagh O'Nial, a nephew of the first Earl of Tyrone, but being advanced in years and of a peaceable disposition, he suffered it to be wrested from him by Hugh, the son of Matthew O'Nial, who, after performing some services to the English in the war against Desmond, was admitted to the title and rank of Earl of Tyrone and to the estate of his ancestors, in virtue of the grant made to his grandfather; a fort on the Blackwater being the only place excepted from his jurisdiction. He afterwards became one of the bitterest and most formidable enemies of the English. In consequence of alleged grievances, he raised forces and suddenly seized on the above-named fort, which was the key of his territory on that side; but being hard pressed by Sir John Norris, he evacuated that position, burnt the town of Dungannon, and the neighbouring villages, together with the greater part of his own fortress there, and endeavoured to preserve his life by concealment. Afterwards, being buoyed up with promises of succours from Spain, he joined a league of all the northern chieftains against the English. In 1597, the whole of Ulster, except the castles along the coast, was in the possession of O'Nial or his adherents; and in an attempt made to relieve the fort of the Blackwater, then hard pressed by his army, Sir Henry Bagnall, Marshal of the English, his inveterate enemy, was utterly routed and slain. After having baffled the celebrated and unfortunate Earl of Essex by a succession of affected submissions and unexpected hostilities, and joined in the expedition to Munster to aid the Spaniards at Kinsale, he was invaded in turn by the royal forces under Lord Mountjoy, who, by seizing on the passes and erecting forts at Charlemont, Mountjoy, and other important positions, reduced him to such extremities that he surrendered at Mellifont, and attended Mountjoy to Dublin, who proposed to send him thence to the Queen. Her death changed his destination for that time; but in the beginning of the ensuing reign, being suspected of an attempt to excite a new insurrection in Ulster, he fled to Spain; and his princely property being consequently confiscated, was parcelled out into six counties, which were modelled, divided, and planted with English settlers under special instructions from the king. According to the rules of his settlement, the whole county, which was estimated to contain 1571 balliboes, or 98,187 acres, being at the rate of 1000 acres to 16 balliboes, was divided into 78 portions, which, after deducting a portion for the church and some lands for Trinity College, Dublin, were granted to English and Irish undertakers, that is, settlers, who engaged to build, fortify, and stock the lands with British tenantry. Five borough towns, Dungannon, Clogher, Omagh, Strabane, and Mountjoy were allowed a certain portion of the surrounding grounds; and another portion was assigned to some of the members of the O'Nial family. The Irish were distributed as tenants among the undertakers, the swordsmen excepted, who were to be removed to the waste parts of Connaught or Munster, where they were to be dispersed and not suffered to settle together in one place. On an inspection of the progress of the plantation, made by Captain Pynnar under the king's direction in 1618, it appeared that the county was divided into the five precincts of Strabane, Omy, Clogher, Mountjoy, and Dungannon: the first of these, Strabane, was allotted to Scotch undertakers, of whom those then in possession of the lands granted to the original patentees were the Earl of Abercorn, Sir Geo. Hamilton, Sir William Stewart, Sir Robert Newcomen, and Sir John Drummond; Omy, allotted to English undertakers, was in the possession of the Earl of Castlehaven and Sir John Davies; Clogher, also allotted to English undertakers, was held by Lord Ridgwaie, George Ridgwaie, Sir Gerard Lowther, Lord Burleigh, John Leigh, Sir William Stewart, Sir William Cope, and William Parsons; Mountjoy, allotted to Scotch undertakers, was held by Sir Robert Heyburne, Lord Vehiltree, Captain Sanderson, Mrs, Lindsey, Alex. Richardson, Andrew Stewart (son to Lord Vehiltree), and David Kenedaie ; Dungannon, allotted to servitors and natives, was held by Lord Chichester, Lord Ridgwaie, Sir Toby Caulfield, William Parsons, Sir Francis Ansley, Lord Wingfield, and Tirlagh O'Nial, The only towns in the erection of which any progress had been made were those of Strabane and Augher. The county continued to improve during the reign of Jas. I, and in the commencement of that of Chas. I., but it suffered greatly during the war of 1641, at the termination of which, much of the lands fell into the hands of new proprietors; and in the subsequent war of 1688 it was the scene of many military events connected with the siege of Londonderry.
Transcribed from A Topographical Dictionary of Ireland, 1840 by Samuel Lewis