The 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 300 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 O'Dea is normally pronounced oh-dee, and sometimes oh-day, in English. Clan descendants may have the surnames Alday, Allday, O'Dea, Dea, Day, O'Day, Dee, 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:
“ 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 English Day was regarded as synonymous." 
The O'Deas, together with the O'Quinns (Irish: Ó Cuin), belong to the Uí Fearmaic group, but it is not known if this kindred belongs to the Dál gCais or to the Uí Fidgenti. Another possibility are the Corcu Baiscind.
- Brian O'Dea - Cannabis smuggler; television and film producer; author.
- 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.
- Dorothy Day - Journalist, social activist, distributist, and anarchist.
- Edward John O'Dea (1856–1932). Bishop of dioceses Nesqually and Seattle.
- Fabian O'Dea - Former Lieutnant Governor of Newfounland, Canada.
- Jimmy O'Dea - Actor, comedian.
- Judith O'Dea - Hollywood actress.
- Paul O'Dea - American professional basketball player.
- Thomas O'Dea (1858–1923). Bishop of Clonfert, Galway, and Kilmacduagh.
- Marcus O'Day - Physicist with crater named after him on the moon.
- 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 2010-08-03.
- ^ Mollaneen townland at the Irish Placenames Database, logainm.ie. Retrieved 2010-08-03.
- ^ Map of Dysert and Mollaneen at Ordnance Survey Ireland. Select Historic 6" option to see old townland boundaries. maps.osi.ie. Retrieved 2010-08-03.
- ^ Irish Families: Their Names, Arms and Origins, by Edward MacLysaght. Dublin: Hodges Figgis 1957, rev. 1972, page 112.
- ^ Surnames of Ireland, by Edward MacLysaght. Shannon: Irish UP 1969.
- ^ The Kingdom of Thomond
- ^ "Bishop Cornelius O'Dea". Diocese of Limerick. http://www.limerickdioceseheritage.org/Diocese/ODea.htm. Retrieved 2009-12-01.
- ^ "Bishop Cornelius O'Dea". catholic-hierarchy.org (unofficial site). http://www.catholic-hierarchy.org/bishop/bodeac.html. Retrieved 2009-12-01.
- ^ Connor O'Dea, Bishop of Limerick (poem). The Irish Monthly, Vol. 49, No. 582 (Dec., 1921). JSTOR 20505775.
- ^ "Bishop Edward John O'Dea". catholic-hierarchy.org (unofficial site). http://www.catholic-hierarchy.org/bishop/bodea.html. Retrieved 2010-05-05.
- ^ "Bishop Thomas O'Dea". catholic-hierarchy.org (unofficial site). http://www.catholic-hierarchy.org/bishop/bodeat.html. Retrieved 2010-05-05.
- O'Dea: Ua Deághaidh: The Story of a Rebel Clan, by Risteárd Ua Cróinín (Richard Cronin), Ballinakella Press, Whitegate, Co. Clare, Ireland, 1992. ISBN 0946538077.
- Irish Battles - A Military History of Ireland, by G.A. Hayes-McCoy, Appletree Press, 1990, ISBN 086281250X
Wikimedia Foundation. 2010.