Quick answer: Casey and O’Casey are recorded anglicized forms of the Irish surname Ó Cathasaigh, meaning “descendant of Cathasach.” Patrick Woulfe glosses the personal name Cathasach as vigilant or watchful. His surname reference records six separate Ó Cathasaigh families, from north County Dublin to Limerick, Cork, Mayo, Roscommon and Fermanagh.
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What does the Casey surname mean?
Woulfe records Ó Cathasaigh with the anglicized forms O’Casey and Casey. The surname means descendant of Cathasach, a personal name he explains as vigilant or watchful. The spelling Casey became widespread in English-language records, while O’Casey preserves the anglicized O’ prefix.
Regional Casey families in Ireland
Woulfe records Ó Cathasaigh families in ancient Meath in the north of present-day County Dublin, Coshlea in County Limerick, the Mitchelstown area of County Cork, Tirawley in County Mayo, County Roscommon and Devenish in County Fermanagh. These regional histories give Casey researchers several useful places to investigate when family records identify a county or parish.
Where were Ó Cathasaigh families recorded?
- Ancient Meath / north County Dublin: Woulfe records an Ó Cathasaigh family as lords of Saithne until Hugh de Lacy dispossessed them.
- County Limerick: a Dalcassian family is recorded in Coshlea.
- County Cork: another family is associated with the area near Mitchelstown.
- County Mayo: an Ó Cathasaigh family is recorded in Tirawley and connected with Kilarduff.
- County Roscommon: Woulfe records a family associated with Cloondara and Tisrara.
- County Fermanagh: another family is recorded in connection with Devenish.
Seán O’Casey and the surname
The best-known modern bearer is the Dublin playwright Seán O’Casey. The Dictionary of Irish Biography records that he was born John Casey in Dublin in 1880 and later used the Irish form Seán Ó Cathasaigh before becoming known as Seán O’Casey.
How to research a Casey or O’Casey family line
Start with the most recent confirmed relatives and work backward through civil, church and census records. Record exact spellings, addresses, parishes and townlands, because each of the six Casey homelands has its own records.
- Search both Casey and O’Casey where record systems allow variant spellings.
- Use the National Archives of Ireland census collections to place known relatives in a specific household and locality.
- Use IrishGenealogy.ie for civil and church records where available.
- Compare the earliest confirmed locality with the regional Ó Cathasaigh references above, then follow the household through successive records.
- When several Casey households appear in one parish, compare parents, sponsors, witnesses and addresses to distinguish them.
Sources and further research
Patrick Woulfe, Irish Names and Surnames: Ó Cathasaigh
National Archives of Ireland: Census records