The O'Dea clan, also found as
O'Day, Dea, or 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==