McLoughlin is an Irish surname.
The surname Mac/Nic Lochlainn originated in the Irish province of Ulster. Lochlann was originally a name for Scandinavia, especially Norway, so called after the fjords – Lochlainn, the adjectival form, literally means "lake-ish" or "full of lakes," a "land of lakes," etc. The Annals of Ulster refer to the Vikings as Lochlannach meaning "of Lochlann."[1] A small DNA sample size; so far, shows the clans origins are in Donegal[2]
Lochlan(n)/Lochlain(n) is still used as a man's personal name in Ireland and Scotland, though not commonly. English forms of the surname Mac/Nic Lochlainn are concentrated in western Ulster, on both sides of the international boundary. But the family are found throughout Ulster, and spread eastward during the Middle Ages, across the North Channel into Scotland where they became the Clan MacLachlan. Spellings of the name peculiar to Scotland include McLachlan, McLachlin, and McLauchlan. The Mac/Nic Lochlainn and their Scottish cousins are descendants of the Northern Uí Néill.[3]
The Ó/Ní Maoilsheachlainn surname originated in Meath. The family claim descent from High King Máel Sechnaill mac Domnaill of the Southern Uí Néill, relatives of the Northern family. The surname was originally rendered O'Melaghlin in Norman French and Middle English but was corrupted to McLoughlin and M'Loughlin in the 18th century.[4]
The Lochnaigh family in Connaught, who claim descent from the Uí Fiachrach dynasty, mostly became Loughney in English but are very occasionally called McLoughlin. They tend to be concentrated in Galway.
The McLoughlins of Ulster are part of the Cenél nEógain branch of the Northern Uí Néill. They ruled what is now Counties Tyrone, Londonderry and Donegal. High Kings of Ireland from this family were:
The Ó Maoilsheachlainns of the Kingdom of Mide (presently the counties of Meath, Westmeath, and parts of the counties of Dublin, Kildare, Offaly, Longford, and Louth, all now in Leinster, and part of County Cavan, now in Ulster) are descendants of the Southern Uí Néill.
High Kings of Ireland of this family included:
The Ó Máoilsheáchlainns of Meath lost their lands and their power in the centuries following the Norman Invasion – their homeland of Meath even losing its status as a kingdom/province and being absorbed into Leinster. The family were recorded as O'Melaghlin, and after the 17th century, McLoughlin.
The Northern Uí Néill family expanded from Ulster into Argyll, in Scotland, where Middle Irish Mac/Nic Lochlainn became Modern Scots Gaelic Mac/Nic Lachlainn, most commonly spelled MacLachlan in Scots and English.
See the Clan MacLachlan article for more information.