**Irish Last Names Starting with O:** A Comprehensive Guide

Looking for an Irish last name that starts with the letter "O"? You've come to the right place! This comprehensive list delves into the rich history and meanings behind some of the most popular and unique Irish surnames beginning with "O." From the common O'Brien to the less familiar O'Driscoll, discover the origins and significance of these traditional names, and perhaps find the perfect one for yourself or your family.
1. **O'Brien:** Descendant of Brian Boru, a legendary Irish king.
2. **O'Connell:** Descendant of Connell, a common Irish name.
3. **O'Connor:** Descendant of Conchobhar, an ancient Irish king and hero.
4. **O'Neill:** Descendant of Niall of the Nine Hostages, a legendary Irish high king.
5. **O'Reilly:** Descendant of Raghallach, an Irish chieftain.
6. **O'Donnell:** Descendant of Domhnall, a common Irish name.
7. **O'Sullivan:** Descendant of Suibhne, an Irish chieftain.
8. **O'Moore:** Descendant of Muircheartach, an Irish king.
9. **O'Callaghan:** Descendant of Callaghan, a common Irish name.
10. **O'Doherty:** Descendant of Doire, an Irish name meaning "oak."
11. **O'Carroll:** Descendant of Cathal, an Irish king.
12. **O'Shaughnessy:** Descendant of Seán, an Irish name meaning "John."
13. **O'Meara:** Descendant of Amhlaoibh, an Irish name meaning "wolf."
14. **O'Hanlon:** Descendant of Anluan, an Irish chieftain.
15. **O'Toole:** Descendant of Tuathal, an Irish high king.
16. **O'Flaherty:** Descendant of Flaithbheartach, an Irish chieftain.
17. **O'Grady:** Descendant of Gráinne, an Irish queen.
18. **O'Dwyer:** Descendant of Dubhghall, an Irish name meaning "dark stranger."
19. **O'Brien:** Descendant of Brian Boru, a legendary Irish king.
20. **O'Malley:** Descendant of Máel-Muire, an Irish name meaning "devotee of Mary."
21. **O'Mahony:** Descendant of Máonach, an Irish chieftain.
22. **O'Nolan:** Descendant of Nuallán, an Irish name meaning "little champion."
23. **O'Rourke:** Descendant of Rúaidhrí, an Irish name meaning "red king."
24. **O'Higgins:** Descendant of Ógán, an Irish name meaning "young."
25. **O'Farrell:** Descendant of Fearghal, an Irish name meaning "man of strength."
26. **O'Loughlin:** Descendant of Lochlainn, an Irish name meaning "from Loughlin."
27. **O'Hehir:** Descendant of Ó hEithir, an Irish name meaning "from the heather."
28. **O'Shea:** Descendant of Ó Seacháin, an Irish name meaning "descendant of Seán."
29. **O'Riordan:** Descendant of Riordáin, an Irish name meaning "red king."
30. **O'Driscoll:** Descendant of Diarmaid, an Irish name meaning "godly."
31. **O'Donovan:** Descendant of Donnchadh, an Irish name meaning "dark warrior."
32. **O'Boyle:** Descendant of Ó Baoill, an Irish name meaning "son of Boyle."
33. **O'Connor:** Descendant of Conchobhar, an ancient Irish king and hero.
34. **O'Brien:** Descendant of Brian Boru, a legendary Irish king.
35. **O'Neill:** Descendant of Niall of the Nine Hostages, a legendary Irish high king.
36. **O'Reilly:** Descendant of Raghallach, an Irish chieftain.
37. **O'Donnell:** Descendant of Domhnall, a common Irish name.
38. **O'Sullivan:** Descendant of Suibhne, an Irish chieftain.
39. **O'Moore:** Descendant of Muircheartach, an Irish king.
40. **O'Callaghan:** Descendant of Callaghan, a common Irish name.
41. **O'Doherty:** Descendant of Doire, an Irish name meaning "oak."
42. **O'Carroll:** Descendant of Cathal, an Irish king.
43. **O'Shaughnessy:** Descendant of Seán, an Irish name meaning "John."
44. **O'Meara:** Descendant of Amhlaoibh, an Irish name meaning "wolf."
45. **O'Hanlon:** Descendant of Anluan, an Irish chieftain.
46. **O'Toole:** Descendant of Tuathal, an Irish high king.
47. **O'Flaherty:** Descendant of Flaithbheartach, an Irish chieftain.
48. **O'Grady:** Descendant of Gráinne, an Irish queen.
49. **O'Dwyer:** Descendant of Dubhghall, an Irish name meaning "dark stranger."
50. **O'Malley:** Descendant of Máel-Muire, an Irish name meaning "devotee of Mary."