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O'Dea/O'Day/Dee (DNA) Project

  • 144 members

About us

Welcome to the home page of the O'Dea/O'Day/Dee (DNA) Project, which you can find at

Surname history

For a full surname history, see the book O'Dea: Ua Déaghaidh: The Story of a Rebel Clan, by Risteárd Ua Cróinín, published in 1992 by Ballinakella Press in Whitegate, County Clare, Ireland (ISBN 0 946538 07 7).

Ua Cróinín writes that the
O'Deas were one of the first families in Europe to have a surname, which they adopted before King Brian Boru made it compulsory early in the 11th century (p. XII);
and that the
chief who gave his own personal name to Clan O'Dea was Déaghaidh (pronounced Day) who is referred to in Keating's History of Irelandunder the year 934 A.D. (p. 12).
Ua Cróinín's pedigree on pp. 6-8 (like that by O'Hart) shows Déaghaidh (or Deadha) as a 14th generation descendant of Cas, making the O'Deas, in theory, a branch of the Dal gCais, or descendants of Cas, who was also reputed to be ancestor of the O'Briens, MacNamaras and related surnames.

According to O'Hart, Deadha had three sons:
  1. Conn Mór, who was ancestor of Muintir Cuinn or Quinn of Munster;
  2. Donoch, who was ancestor of the O'Deas; and
  3. Flaithertach, was the ancestor of Roughan.
Hence, we expect to find Y-DNA matches between O'Deas, Quinns and Roughans, and welcome related bearers of the latter surnames to this project.

Having adopted the surname, the
O'Deas became lords of that part of North West Clare between the River Fergus to the East, the Burren to the North and the Atlantic Ocean to the West (p. 9).
The leading authorities on Irish surnames give more succinct histories of the surname. According to MacLysaght, O'Dea, or in Irish Ó Deaghaidh or Ó Deághaidh or Ó Deá, is the surname of one of the principal Dalcassian septs, common in Thomond (now County Clare). Seán de Bhulbh writes that there were septs in Clare and Tipperary.

Hence one could expect many O'Deas to have a similar genetic signature to those of other Dalcassian surnames.

Away from its homeland, where it is often pronounced "O'Day", the surname is usually pronounced as "O'Dee", leading to potential confusion with Ó Diaghaidh, which is a distinct name. MacLysaght notes that, as Dia is the Irish word for God, this accounts for the use of Godwin in County Mayo as a synonym.

The O' prefix is now almost always used, but in the 19th century Dea was quite usual and the English Day (which has a separate FTDNA project) was regarded as synonymous. Another occasional synonym is Daw.

The surname has since spread throughout Ireland and abroad. The 1911 census of Ireland included 1,324 O'Deas, just over half of them (683) born in County Clare and another 242 born in County Limerick.

For more information on the surname, see the Clare County Library website or Wikipedia.

The Dysert O'Dea Clan Association

This DNA project is being operated in conjunction with the Dysert O'Dea Clan Association, which organises triennial gatherings in Ireland, of which the 10th in May 2018 coincided with the 700th anniversary of the Battle of Dysert O'Dea in 1318, in which the Irish side was led by Conor O'Dea.
For more details, including the dates of future gatherings in Ireland and elsewhere, see the association's website.

Project administrators

The project administrators are James O Dea of the Dysert O'Dea Clan Association and genetic genealogist Paddy Waldron (GGGGgrandson of a female O'Dea).
The project was established on 16 July 2017 and a circular e-mail encouraging Dysert O'Dea Clan Association members to join the DNA project was sent on 18 October 2017.
The project administrators are involved in organising the triennial O'Dea Clan Gatherings.
The 2018 Gathering schedule included a talk about the O'Dea/O'Day/Dee DNA Project by Paddy Waldron in the Banner Room at the Old Ground Hotel in Ennis, County Clare, on Friday 11 May 2018 at 10:30am. The talk can be viewed on YouTube.
Paddy Waldron's personal website has a great deal of useful additional reading on genetic genealogy, such as How to get the most out of your DNA results and Interpreting Y-DNA results.

How to participate

  1. If you are not already a project member and you have any ancestor with the surname O'Dea (or a variant spelling), then please JOIN the project by clicking on the JOIN button to the right of the shopfront in the banner photograph above. However, if you are not yet an FTDNA customer but have submitted a DNA sample to one of the other DNA companies, then you may be able to copy your data to via the free Autosomal Transfer and should do this before joining any projects.
  2. If you are a male O'Dea and your most distant known male line ancestor is not yet represented on the O'Dea/O'Day/Dee (DNA) Project Y-DNA Colorized Chart, then please order whatever level of Y-DNA analysis your budget allows.
  3. If you are a female, then please also recruit a male O'Dea descended from your most distant known male line ancestor to the project.
  4. If your O'Dea lineage is already represented in the project or if it has "daughtered out", then you can donate to the project here to fund more advanced Y-DNA analysis of existing DNA samples. These donations can be used only to purchase DNA analysis from FTDNA. This project appears as both O'DEA O'DAY GROUP and O'DEA/O'DAY/DEE PROJECT on the dropdown menu on the Group General Fund Contribution page.
  5. In order that you and the other members can benefit from your membership of the project, it is imperative that you squeeze in names, dates and places to the 50 characters allowed for both your Direct Maternal (i.e. matrilineal) and Direct Paternal (i.e. patrilineal) Most Distant (i.e. most distant known) Ancestors under the Earliest Known Ancestors tab here in order to help those looking for mitochondrial DNA matches and Y-DNA matches respectively; and that you also upload a GEDCOM file here showing your direct ancestors (which should automatically populate your surname list, although this was not working in late 2019 and early 2020).
  6. In order to achieve the full benefits of project membership, you must take action to give the project administrators "Limited" or "Advanced" access to your kit. This can be done when you join or can be done later by clicking here. For each project that you have joined, click the pencil icon, scroll down and if necessary select "Advanced" or "Limited" instead of "Minimum" from the relevant dropdowns, then click ACCEPT PROJECT PREFERENCES and then click CONFIRM.
  7. If you want to see which of your Family Finder matches are in this project (or in any project that you have joined), then just go to the Advanced Matches page, login if necessary and tick the Family Finder checkbox, select the project in the "Show Matches For" dropdown and click the RUN REPORT button. Finally, click the Family Finder column heading to sort the matches by closeness of estimated relationship.
  8. If you have received Big Y-700 (or Big Y-500 or Big Y) results and belong to either of the main branches of haplogroup R (R-P312 or R-U106), then please copy your results to The Big Tree by following these instructions and uploading here.
  9. For a discussion of the latest results, see here.
  10. Please feel free to use the Activity Feed to direct any questions that you may have to the project administrators and for discussion with other project members.

Last updated 15 March 2020.