Which Irish surnames descend from Brian Boru or share his Dál gCais kindred: O’Brien, MacMahon, Considine, Kennedy, MacNamara, O’Grady, Hogan, O’Meara, McGrath, Clancy, McInerney, O’Dea, Hurley, Gleeson and Casey.

Only a few surnames on this list descend from Brian Boru himself: O’Brien and the Clare MacMahons, plus the Considines and one branch of the O’Deas. 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.

Family Tree DNA test kit
Early Bird Sale until 11 November: Family Finder $39, Y-37 $79, Y-111 $189, Big Y-700 $399 (USD)
Recommended DNA test
Which Dál gCais family is yours?
Family Tree DNA is the only major testing company with dedicated Y-DNA tests, and it hosts the R-L226 and surname projects that sort the O’Briens, MacNamaras, Kennedys and other Dalcassian families into their branches.
  • Y-37: shows whether your paternal line fits the Irish Type III (R-L226) pattern.
  • Big Y-700: places you on a specific branch of the tree, the test that project administrators recommend.
  • Family Finder: covers all your family lines, not just the male line, and finds cousins from the last five or six generations. Women can take it too.
  • Free projects: once tested, join the R-L226 project and your own surname project to compare results.
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When you order: Mac names are listed as Mc with a space, such as “Mc Namara” and “Mc Mahon”.
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Surname Relationship to Brian Boru Homeland
O’Brien Direct descendants Clare (Thomond)
MacMahon (Clare) Direct descendants, via his great-grandson Muirchertach South-west Clare
Considine Direct descendants, via a 12th-century Bishop of Killaloe Clare
Kennedy Descended from his brother Donncuan East Clare, then north Tipperary
Hogan Descended from his uncle North Tipperary
O’Meara Dál gCais kindred Toomevara, north Tipperary
Hurley Dál gCais kindred (Thomond line only); Cork Hurleys are unrelated Thomond, then Knocklong, Limerick
McGrath Dál gCais by tradition; hereditary poets to his descendants Clare
MacNamara Distant cousins, Uí Caisín branch East Clare
Clancy A MacNamara branch; brehons to his descendants (Clare line only) North-west Clare
McInerney A MacNamara branch (Clare line only) East Clare
O’Grady Distant cousins, Uí Caisín branch East Clare, then Limerick
O’Dea Dál gCais kindred; one branch carries O’Brien DNA Dysert O’Dea, Clare
Gleeson Not in the old pedigrees, but one DNA lineage is Dál gCais Ormond and Arra, north Tipperary
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 Family Tree DNA’s Family Finder 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.