O'Dea Clan Origins
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 at the 80-acre (320,000 m2) townland of Dysert O'Dea (Irish: Dísert, meaning "hermitage"). 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"), near Corofin. ( )
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.
|“||O'Dea is a name associated alike in the past and at present almost exclusively with the County Clare and the areas such as Limerick City and North Tipperary which immediately adjoin it. It is not a common name anywhere and even in County Clare is not numerous outside the part of the county where it originated. This is indicated by the place names Tully O'Dea and Dysart O'Dea, the site of a famous battle in 1318. The head of the sept was chief of a considerable territory comprising much of the barony of Inchiquin. In Irish the name is Ó Deághaidh.||”|
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  was regarded as synonymous."
- AI1123.7 Muiredach Ua Dedaid was slain by Tadc, son of Diarmait.
- Addison O'Dea -- Documentary filmmaker
- Chris O'Dea – American documentary filmmaker.
- Cornelius (Connor) O'Dea. Bishop of Limerick. (Appointed 1400; resigned 1426).
- Darren O'Dea – Irish footballer.
- Denis O'Dea – Actor and father of Donnacha, below.
- Donnacha O'Dea – Olympic swimmer and professional poker player.
- Edward John O'Dea (1856–1932). Bishop of dioceses Nesqually and Seattle.
- Fabian O'Dea – Former Lieutenant Governor of Newfoundland, Canada.
- Jimmy O'Dea – Actor, comedian.
- Judith O'Dea – Hollywood actress.
- Kevin O'Dea – American football coach.
- Louis O'Dea – Irish politician elected to Dáil Éireann and Seanad Éireann between 1923 and 1944.
- Luke O'Dea – Irish rugby player.
- Michael O'Dea – Irish Senator from 1922 to 1925.
- Oliver O'Dea – Irish professional boxer.
- Oscar O'Dea – Young English long jumper , who does parkour and coding.
- Pat O'Dea – Australian and American football player and coach.
- Paul O'Dea – American professional basketball player.
- Thomas O'Dea (1858–1923). Bishop of Clonfert, Galway, and Kilmacduagh.
- Thomas F.O'Dea (1915-1974) – American sociologist of religions.
- Willie O'Dea – Irish politician.
See also the O'Day page for a listing of O'Days.
- 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.
- Dysert townland at the Irish Placenames Database, logainm.ie. Retrieved 3 August 2010.
- Mollaneen townland at the Irish Placenames Database, logainm.ie. Retrieved 3 August 2010.
- 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.
- Irish Families: Their Names, Arms and Origins, by Edward MacLysaght. Dublin: Hodges Figgis 1957, rev. 1972, page 112.
- "Day (surname) - Wikipedia". en.m.wikipedia.org. Retrieved 19 July 2018.
- Surnames of Ireland, by Edward MacLysaght. Shannon: Irish UP 1969.
- O'Laughlin, Michael C. Families of County Clare Ireland. Irish Genealogical Foundation. ISBN 978-0940134980.
- "Bishop Cornelius O'Dea". Diocese of Limerick. Retrieved 1 December 2009.
- "Bishop Cornelius O'Dea". catholic-hierarchy.org (unofficial site). Retrieved 1 December 2009.
- "Connor O'Dea, Bishop of Limerick (poem)". The Irish Monthly. 49: 507–509. December 1921. JSTOR 20505775.
- "Bishop Edward John O'Dea". catholic-hierarchy.org (unofficial site). Retrieved 5 May 2010.
- "Bishop Thomas O'Dea". catholic-hierarchy.org (unofficial site). Retrieved 5 May 2010.
- O'DEA, THOMAS F. Encyclopedia of Religion and Society. Retrieved: 2019-01-08.
- 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