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O'Dea (/ˈd/, oh-DAY; Irish: Ó Deá ([oːˈdʲeː]), contraction of Ó Deághaidh, formerly Ua Deághaidh), is an Irish surname derived from Deághaidh, the name of a tenth-century clan chieftain.

O'Dea Clan Origins[edit]

The Ó Deá /O'Dea clan came originally from County Clare where there is a fortified tower house over 500 years old known as O'Dea Castle[1] at the 80-acre (320,000 m2) townland of Dysert O'Dea (Irish: Dísert, meaning "hermitage").[2] The ruins of Dysert O'Dea Monastery, round tower, and St. Tola's high cross are 265 metres to the south-southwest of the castle in the adjacent 260-acre (1.1 km2) townland of Mollaneen (Irish: Molainín, meaning "the little hill"),[3] near Corofin.[4] (52°54′41″N 9°03′59″W / 52.911361°N 9.066381°W / 52.911361; -9.066381)

The name Ó Deá is normally pronounced "oh-daa" while the anglicised form O'Dea is normally pronounced oh-dee, and sometimes oh-day. Clan descendants may have the surnames Alday, Allday, O'Dea, Dea, Deas, Day, Daye, O'Day, O'Daye, Dee, Dees, O'Dee, Godwin, or Goodwin.

Edward MacLysaght, the former Chief Herald of Ireland, writing in his book, Irish Families, began his discussion of the O'Dea family as follows:

In another book, The Surnames of Ireland, MacLysaght describes the O'Deas as "one of the principal Dalcassian septs", and about the name itself, he remarks, "The prefix O is now almost always used, but a century ago Dea was quite usual and the surname Day [6] was regarded as synonymous."[7]


The O'Deas, together with the O'Quinns (Irish: Ó Cuinn) and the O'Griffins (Irish: Ó Gríofa), belong to the Uí Fearmaic group. [8]

Annalistic references[edit]

  • AI1123.7 Muiredach Ua Dedaid was slain by Tadc, son of Diarmait.


See also the O'Day page for a listing of O'Days.

See also[edit]


  1. ^ Dysart O'Dea Castle, Co. Clare by Risteard Ua Croinin and Martin Breen, The Other Clare, Volume 9, page 17. Shannon Archaeological and Historical Society, April 1985.
  2. ^ Dysert townland at the Irish Placenames Database, logainm.ie. Retrieved 3 August 2010.
  3. ^ Mollaneen townland at the Irish Placenames Database, logainm.ie. Retrieved 3 August 2010.
  4. ^ Map of Dysert and Mollaneen at Ordnance Survey Ireland. Select Historic 6" option to see old townland boundaries. maps.osi.ie. Retrieved 3 August 2010.
  5. ^ Irish Families: Their Names, Arms and Origins, by Edward MacLysaght. Dublin: Hodges Figgis 1957, rev. 1972, page 112.
  6. ^ "Day (surname) - Wikipedia". en.m.wikipedia.org. Retrieved 19 July 2018.
  7. ^ Surnames of Ireland, by Edward MacLysaght. Shannon: Irish UP 1969.
  8. ^ O'Laughlin, Michael C. Families of County Clare Ireland. Irish Genealogical Foundation. ISBN 978-0940134980.
  9. ^ "Bishop Cornelius O'Dea". Diocese of Limerick. Retrieved 1 December 2009.
  10. ^ "Bishop Cornelius O'Dea". catholic-hierarchy.org (unofficial site). Retrieved 1 December 2009.
  11. ^ "Connor O'Dea, Bishop of Limerick (poem)". The Irish Monthly. 49: 507–509. December 1921. JSTOR 20505775.
  12. ^ "Bishop Edward John O'Dea". catholic-hierarchy.org (unofficial site). Retrieved 5 May 2010.
  13. ^ "Bishop Thomas O'Dea". catholic-hierarchy.org (unofficial site). Retrieved 5 May 2010.
  14. ^ O'DEA, THOMAS F. Encyclopedia of Religion and Society. Retrieved: 2019-01-08.

Further reading[edit]

  • O'Dea: Ua Deághaidh: The Story of a Rebel Clan, by Risteárd Ua Cróinín (Richard Cronin), Ballinakella Press, Whitegate, Co. Clare, Ireland, 1992. ISBN 0-946538-07-7.
  • Irish Battles – A Military History of Ireland, by G.A. Hayes-McCoy, Appletree Press, 1990, ISBN 0-86281-250-X

External links[edit]