Which Irish surnames descend from Brian Boru or share his Dál gCais kindred: O’Brien, MacMahon, Kennedy, MacNamara, O’Grady, Hogan, McGrath and Casey.
Only two surnames on this list descend from Brian Boru himself: O’Brien and the Clare MacMahons. The others belong to his wider kindred, the Dál gCais of north Munster, and descend from his brothers, uncles or more distant cousins. Men of all these families commonly share the Y-DNA marker R-L226, also called Irish Type III.
| Surname | Relationship to Brian Boru | Homeland |
|---|---|---|
| O’Brien | Direct descendants | Clare (Thomond) |
| MacMahon (Clare) | Direct descendants, via his great-grandson Muirchertach | South-west Clare |
| Kennedy | Descended from his brother Donncuan | East Clare, then north Tipperary |
| Hogan | Descended from his uncle | North Tipperary |
| McGrath | Dál gCais by tradition; hereditary poets to his descendants | Clare |
| MacNamara | Distant cousins, Uí Caisín branch | East Clare |
| O’Grady | Distant cousins, Uí Caisín branch | East Clare, then Limerick |
| Casey | Some lines only; most Caseys are unrelated | Several unrelated origins |
A surname is a clue, not proof
Surnames became fixed in Ireland from around the 10th and 11th centuries, and over a thousand years they drifted through adoptions, name changes and families taking a local lord’s name. Several of these surnames also have unrelated namesakes, such as the Monaghan MacMahons or the Galway Kennedys. A Y-DNA test is the only way to confirm a paternal link to the Dál gCais, and an autosomal test such as AncestryDNA helps build the paper trail. Our Brian Boru descendants and DNA guide explains both.
Visiting the family homeland? The Brian Boru trail covers Killaloe and the wider route, and you can see the lake country of the Dál gCais from the water with a Lough Derg cruiser. For the heraldry these families share, see the O’Brien coat of arms explained.