Throughout the world, O'Callaghan (O'Callaghan 
, О'Каллаган 
) is a very rare male given name. The first name O'Callaghan is habitual in Australia and New Zealand, particularly Australia, where it is a very rare boy's name. Predominantly, O'Callaghan is the last name as well as the forename.
| VARIANT | COUNTRY |
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| O'Callaghan | Canada, Australia, United States, Ireland, United Kingdom |
| О'Каллаган | Ukraine |
Callaghan, Ò'Callaghan, and Каллаган
| donat o'callaghan (born 1789) (b. 1789) |
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| sir desmond dykes tynte o'callaghan (1843-1931), Major-General (b. 1843) |
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| loghlen o'callaghan, the o'callaghan Peerage person ID=543518 |
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| unknown daughter o'callaghan Peerage person ID=543617 |
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| callaghan o'callaghan Peerage person ID=543642 |
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| cahir o'callaghan Peerage person ID=543662 |
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| morogh o'callaghan Peerage person ID=543714 |
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| teige o'callaghan Peerage person ID=543542 |
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| cahir o'callaghan Peerage person ID=543565 |
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| owney o'callaghan Peerage person ID=543569 |
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| cahir o'callaghan Peerage person ID=543577 |
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| cahir o'callaghan Peerage person ID=543591 |
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| maccraith o'callaghan Peerage person ID=543647 |
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| callaghan o'callaghan Peerage person ID=351028 |
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| mahon o'callaghan, the o'callaghan Peerage person ID=543516 |
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