A leading family of the Cenel nEogain branch of the northern U Neill dynasty, the Meic Lochlainn (Mac Loughlin) were descended from Lochlann mac Maelsechnaill, king of Inishowen, who died in 1023. There is some confusion among the medieval genealogists in regard to the ancestry of the Mic Lochlainn, due to a deliberately forged pedigree drawn up during the reign of the high king, Domnall Mac Lochlainn (d. 1121). In reality, the Meic Lochlann were descended from Domnall Dabaill, son of the Cenel nEogain king, Aed Findliath, whose other son was Niall Glundub, ancestor of the Ua Neill dynasty of southern Tfr nEogain. The Meic Lochlainn, who were known as the Clann Domhnaill, were a great warrior family, who suppressed their rivals, the Ua Neills, and then usurped their genealogy. However, they were greatly disadvantaged in wider Irish politics by their distance from the beneficial influence of the Norse towns in southern Ireland.
Domnall Mac Lochlann, (d. 1121), king of Aileach and high king of Ireland for twenty years, foiled the attempts by the Munster high king, Muirchertach Ua Briain, to subdue the Cenel nEogain. By using the good offices of the abbot of Armagh, Domnall continually made peace with Ua Briain from 1099 to 1113. In 1110, Domnall raided Connacht and seized three thousand prisoners and many thousands of cattle. Domnall died in 1121, aged seventy-three, being called "the most distinguished of the Irish for personal form, family, sense, prowess, prosperity and happiness, for bestowing of jewels and food upon the mighty and the needy." His son Niall Mac Lochlainn succeeded him as king of Tfr nEogain.
Domhnall’s grandson, Muirchertach Mac Lochlainn, was high king of Ireland from 1156 to 1166. A powerful king, Muirchertach counted men such as Diarmait Mac Murchada, king of Leinster, among his vassals, and made a policy of dividing rival kingdoms such as Mide, out among subservient claimants. In 1150, Muirchertach granted twenty cattle and a five-ounce gold ring to the abbot of Derry. In 1154, he hired a Norse fleet from the Hebrides and the Isle of Man to oppose the fleet of Tairrdelbach Ua Conchobair, king of Connacht. Muirchertach’s flotilla, however, was defeated in a naval battle off Inishowen. In the same year, Mac Lochlainn obtained the submission of the Norse of Dublin and granted them tuarastal (a ceremonial gift to seal a vassal’s submission) of 1,200 cattle. In 1157, Muirchertach attended the synod of Mellifont granting "seven score cows, and three score ounces of gold, to God and to the clergy" as well as an entire town-land near Drogheda. In 1159, Muirchertach defeated Ruadn Ua Conchobair in a battle at Ardee and in 1162 led an army against the Norse of Dublin, who submitted, paying Mac Lochlainn "six score ounces of gold." Muirchertach was a ruthless king. In 1160, he had the influential Domnall Ua Gairmledaig, lord of Cinel Moen, assassinated. However, in 1166 Muirchertach made a fatal mistake when he blinded Eochaid Mac Duinnsleibe, king of Ulaid. This blinding outraged the north of Ireland, and Mac Lochlainn was abandoned by most of his army. He was defeated and killed by Mac Duinnsleibe’s foster-father and guarantor, Donnchad Ua Cerbaill, king of Airghialla. In his obit, Mac Lochlainn was called "the chief lamp of the valour, chivalry, hospitality, and prowess of the west of the world in his time."
Following Muirchertach Mac Lochlainn’s death, the Ua Neills emerged again as a force to be reckoned with in Tfr nEogain and took the kingship from their Mac Lochlainn rivals. In 1167, the new high king, Ruain Ua Conchobair divided Tfr nEogain in two, north and south of the mountain, between Muirchert-ach’s son, Niall Mac Lochlainn, and Aed "An Maca-oimh Toinleasc" Ua Neill. After the Anglo-Norman invasion of Ulster, the Meic Lochlainn assisted the Ulaid against John de Courcey. In 1196, Muirchertach Mac Lochlainn, king of Tfr nEogain, was noted as a "destroyer of the cities and castles of the English." He was slain in that year by an Ua Cathain, a member of a new rising dynasty in County Derry. In 1215, Aed Mac Lochlainn was killed by the English.
In the early thirteenth century, the Meic Lochlainn began to occupy the ecclesiastical center of Derry but were becoming very unpopular among the Cenel nEogain. In the 1230s, Domnall Mac Lochlainn became very powerful. In 1235, he killed Domnall Ua Neill, the king of Tfr nEogain, and assumed the kingship himself. In 1238, Domnall instigated a Gaelic Irish uprising against Hugh de Lacy, east of the Bann, and in 1239 he was victorious in the battle of Carnteel, fought near Dungannon, against some Ua Neill and Ua Gairmledaig rivals. However, Domnall was crushingly defeated at the battle of Caimeirge (a site traditionally said to be near Maghera in Co. Derry), by Brian Ua Neill and Maelsechnaill Ua Domnaill, king of Tfr Conaill. Domnall and ten other Meic Lochlainn of his derbhfine (close family) were killed. The battle of Caimeirge proved to be decisive in the struggle for power in Tfr nEogain between the Meic Lochlainn and the Ua Neills. Very unusual for Gaelic Ireland, the Mac Lochlainn family was totally eclipsed and never again threatened Ua Neill hegemony of Tfr nEogain. After the battle, Brian Ua Neill married Mac Lochlainn’s daughter, Cecilia, and a Mac Lochlainn chieftain, Diarmaid Mac Lochlainn, was killed at Brian Ua Neill’s great defeat at Down Patrick in 1260.
Nevertheless, the Mac Lochlainns did survive in a very reduced condition in the peninsula of Inishowen. They remained as chieftains but failed to retain the lordship, even of Inishowen, which was taken over first by the Earls of Ulster and then by the powerful Cenel Conaill dynasty of Ua Dochartaigh. In 1375, Sean Mac Lochlainn, "Chief of his own tribe" died, and in 1510 "Mac Lochlainn, Uaithne" died. By the end of the sixteenth century, the Mac Lochlainn chieftains still survived, tributary to Ua Dochartaigh, and held two castles on the shore of Lough Foyle. In 1601, Hugh Carrogh Mac Lochlainn "chief of his sept," held Carrickmaquigley Castle (Red Castle) and Brian Og Mac Lochlainn held Garnigall Castle (White Castle).
