Donough O'Brien, 2nd Earl of Thomond

{{Use dmy dates|date=August 2020}}

{{Use Irish English|date=August 2020}}

{{Infobox nobility

| name = Donough O'Brien

| title = 2nd Earl of Thomond & Baron Ibrackan

| noble family = Ua Briain

| father = Connor O'Brien, King of Thomond

| mother = Annabell Burke

| spouse = Helen Butler

| issue = {{startplainlist}}

• Margaret O'Brien
• Connor O'Brien, 3rd Earl of Thomond
• Donal O'Brien
• Honora O'Brien

{{endplainlist}}

| birth_date = {{Circa|1520}} Deduced from:
• Minor at his father's death at 1540. (below 21) (see History of the O'Briens from Brian Boroimhe, AD. 1000 to AD. 1945, Donough O'Brien, page 61, https://archive.org/details/historyofobriens00obri/page/60/mode/2up)
• Old enough to bear his own son before his death in 1553, who was politically active by 1559.

| death_date = 1 April 1553

}}

Donough O'Brien, 2nd Earl of Thomond ({{langx|ga|Donnchadh Ó Briain}}; died 1 April 1553), also known as "the fat",{{cite book

| editor-last=Cokayne

| editor-first=George Edward

| editor-link=George Cokayne

| year=1896

| title=Complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct or dormant (S to T)

| volume=7

| edition=1st

| page=391

| location=London

| publisher=George Bell & Sons

| url=http://contentdm.lib.byu.edu/u?/FH18,32320

| accessdate=28 December 2011}} was the son of Connor O'Brien, King of Thomond and Annabell Burke. He inherited the earldom from his uncle, Murrough O'Brien, by special remainder.{{Cite EB1911|wstitle=Thomond, Earl and Marquess of|volume=26|page=869}}

O'Brien married Helen Butler, daughter of Piers Butler, 8th Earl of Ormonde and Lady Margaret Fitzgerald. He died on 1 April 1553, after being attacked by his brothers at the family seat of Clonroad. O'Brien's brother Sir Donald was named king of Thomond by the Dalgais, but O'Brien's son, Connor, allied himself with the English and regained control of his lands.{{cite book

| last=O'Donoghue

| first=John

| title=Historical memoir of the O'Briens: with notes, appendix, and a genealogical table of their several branches

| publisher=Hodges, Smith, & Co.

| year=1860

| pages=187–188

| url=https://books.google.com/books?id=1ONrAAAAMAAJ&pg=PA187

| accessdate=28 December 2011}}

Children of Donough O'Brien and Helen Butler:

• Margaret O'Brien (d. 1568) married Dermod O'Brien, 2nd Baron Inchiquin, and Richard Burke, 2nd Earl of Clanricarde{{Cite book |last=Cokayne |first=G. E. |author-link=George Edward Cokayne |title=The Complete Peerage of England, Scotland, Ireland, Great Britain, and the United Kingdom Extant, Extinct, or Dormant |title-link=The Complete Peerage |publisher=George Bell & Sons |year=1889 |edition=1st |volume=2 |location=London}}
• Connor O'Brien, 3rd Earl of Thomond (c. 1534 – 1581)
• Donal or Daniel
• Honora married Teige Macnamara