Casey comes from at least six unrelated Irish families. Which ones there were, how some Caseys connect to Brian Boru’s Dál gCais kindred, and how DNA tells you which is yours.

Casey (Ó Cathasaigh, “descendant of Cathasach”, meaning watchful or vigilant) is not one family but several. At least six unrelated Casey families grew up independently in different parts of medieval Ireland. Some Caseys from north Munster test into the Dál gCais Y-DNA group, Brian Boru’s kindred, but most Caseys have no connection to him. A Y-DNA test is the only way to know which Casey family is yours.

Origin of the name

Cathasach was a popular personal name in early Ireland, which is why several unrelated families ended up with the same surname. Ireland Calls lists the six medieval septs. The two most important were the Lords of Saithne, in what is now the barony of Balrothery West in north County Dublin, and the church stewards (erenaghs) of Devenish in County Fermanagh. The other four were at Liscannon in County Limerick, Mitchelstown in County Cork, Clondara in County Roscommon and Tirawley in County Mayo.

A separate Mac Cathasaigh family belonged to Louth and Monaghan. Over time many of its members adopted O’Casey or plain Casey, blurring the line between the two.

Which Caseys connect to Brian Boru?

Casey is one of the surnames that turns up in R-L226 (Irish Type III), the Y-DNA signature of the Dál gCais, in studies of north Munster families. That points to at least one Casey family belonging to Brian Boru’s kindred.

The Limerick sept at Liscannon, near Bruff, is the most likely candidate on geography alone, as it sat in Dalcassian-influenced country close to the O’Grady seat at Kilballyowen. That link has not been proven, though, and the Dublin, Fermanagh, Cork, Roscommon and Mayo Caseys are unrelated to the Dál gCais. If your family comes from Clare or Limerick, a Dalcassian origin is possible. If it comes from elsewhere, it is unlikely.

Casey DNA: the only reliable answer

With so many unrelated origins, Casey is a surname where DNA does most of the work. A Y-37 test from Family Tree DNA will show which genetic family your paternal line belongs to. If you test positive for R-L226, Big Y-700 can place you among other Dalcassian families. Join the Casey surname project at Family Tree DNA to compare results with other Caseys.

Women and anyone researching other lines should use an autosomal test such as AncestryDNA to build the tree back to the 1800s and find the county your Caseys came from. Our DNA guide covers the Irish records you’ll need.

Famous Caseys

The playwright Seán O’Casey (1880 to 1964), author of Juno and the Paycock, was born John Casey in Dublin and later adopted the Irish form of his name.

Casey places to visit

Because the Casey families are spread across Ireland, there is no single ancestral site. Start with your own family’s county. If DNA points you to the Dál gCais, the Limerick and Clare heartland is the place to go: Kilballyowen near Bruff, then north to Killaloe on our Brian Boru trail.

Related Dál gCais surnames

See the MacNamaras, O’Gradys, Kennedys, Hogans, McGraths and MacMahons, or browse all Brian Boru kindred surnames.

Frequently asked questions

Are all Caseys related?

No. At least six unrelated Casey families existed in medieval Ireland, in Dublin, Fermanagh, Limerick, Cork, Roscommon and Mayo.

Are Caseys related to Brian Boru?

Some are. A north Munster Casey line appears in the Dál gCais Y-DNA group, but most Caseys descend from unrelated families.

What does Casey mean?

It comes from Ó Cathasaigh, “descendant of Cathasach”, a personal name meaning watchful or vigilant.

Is O’Casey the same as Casey?

Yes. O’Casey keeps the original Ó prefix, which many families dropped under English rule.

Sources

1. Ireland Calls, Irish Surname: Casey.
2. Dennis M. Wright, “A Set of Distinctive Marker Values Defines a Y-STR Signature for Gaelic Dalcassian Families”, Journal of Genetic Genealogy 5(1), 2009.
3. Edward MacLysaght, The Surnames of Ireland (Irish Academic Press, 6th edition, 1985).