The Scandinavian settlers of the port towns, remembered in a handful of names.
The Norse built Ireland's first towns (Dublin, Waterford, Wexford, Limerick, Cork were all Viking ports before they were anything else) and then stayed for three centuries, marrying in. The mixed population called themselves Ostmen, the East-men, a name that survives in Oxmantown in Dublin, from Austmanna-tún, the East-men's homestead. By the time the Normans arrived in 1169 the Norse of the towns were a people of their own, neither Scandinavian nor quite Gaelic.
The surnames they left are mostly Gaelic constructions about Norsemen rather than Norse words. Doyle is Ó Dubhghaill, the descendant of the dark foreigner — dubh-gall being what the Irish called a Dane. Gill is Mac an Ghoill, the son of the foreigner. Reynolds is Mac Raghnaill, the son of Rögnvaldr, a Norse personal name that the Irish adopted and put Mac in front of. Cotter, MacIvor and MacAskill are the same pattern in other names.
A second, smaller group came round the long way. Sinnott, Esmonde and Aylward are Norse personal names that had settled in England before the Normans brought them to Wexford, which is why they are marked here as Norse-English rather than Norse-Gaelic. Seven surnames is a small showing for three hundred years of Norse Ireland; it is an honest one. The Ostmen were absorbed, first into Gaelic Ireland and then into the Norman towns, and most of their descendants carry names that give nothing away.
Sources: Wikipedia — Norse–Gaels ↗ · Wikipedia — Kingdom of Dublin ↗
Homelands are the historic heartland of the name, not where the family is now — people moved, and the Famine and the plantations moved them further.
It is a Gaelic name about a Viking. Ó Dubhghaill means the descendant of the dark foreigner (dubh-gall, the Irish term for a Dane) so the founding ancestor was, or was called, a Norseman.
Fewer than you would expect for three centuries of settlement. Doyle, Gill and Reynolds are the best known on this site; Cotter, MacIvor and MacAskill are others. The Norse-English names of Wexford (Sinnott, Esmonde, Aylward) came later, by way of England.
In the port towns they founded: Dublin, Waterford, Wexford, Limerick and Cork. Their mixed descendants called themselves Ostmen, East-men, and Dublin's Oxmantown keeps the word.
7: Aylward, Doyle, Esmonde, Gill, Mitchell, Reynolds, Sinnott.
Most often Wexford (3), Down (2), Waterford (1), Kilkenny (1).