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Last name O Brien (O Brien
) , globally, is quite a common family name. The cognomen O Brien is characteristic of Ireland, where it is quite a common surname, Australia, where it is a rare surname, and the United States. Not in comparison with a country's population, the name is most common in Ireland, the United States, and the United Kingdom.
| VARIANT | COUNTRY |
|---|---|
| O Brien | Australia, Indonesia, United States, Ireland, United Kingdom |