O'Dea ( ; , formerly ), is an Irish surname derived from , the name of a tenth-century clan chieftain. O'Dea clan origins The O'Dea clan, also found as O'Day or just Day, came originally from County Clare in Ireland where there is a fortified tower house over 500 years old known as O'Dea Castle at the townland of Dysert O'Dea (). The ruins of the 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 townland of Mollaneen (), near Corofin. () 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 was regarded as synonymous." Ancestry The O'Deas – together with the O'Quinns () and the O'Griffins () – belonged to the group, which was a branch of the Dalcassian tribe. Notable O'Deas Addison O'Dea – American documentary filmmaker Ann O'Dea – Irish journalist and businesswoman Ben O'Dea – New Zealand beach volleyball player Bob O'Dea – New Zealand rugby player Brian O'Dea – Canadian smuggler and author Cornelius O'Dea – Irish bishop Danny O'Dea – British actor Darrell O'Dea – Canadian musician and recording engineer Darren O'Dea – Irish football manager and player Denis O'Dea – Irish actor Donnacha O'Dea – Irish Olympic swimmer and professional poker player Ebony O'Dea – Australian rules football player Edward John O'Dea – American bishop Ernest Charles O'Dea – Australian politician and union official Fabian O'Dea – Lieutenant Governor of Newfoundland, Canada Jane Skiles O'Dea – American navy officer Jim O'Dea – Australian rules football player Jimmy O'Dea – Irish actor and comedian John O'Dea – American Civil War soldier John R. O'Dea – Canadian businessman and politician Jonathan O'Dea – Australian politician Judith O'Dea – American film actress Ken O'Dea – American baseball player Kevin O'Dea – American football coach Larry O'Dea – Australian wrestler and promoter Louis O'Dea – Irish politician Luke O'Dea – Irish rugby player Luke O'Dea – Australian football player Mark O'Dea – British television presenter Michael O'Dea – Irish politician Michael O'Dea – Australian politician