Cognomen O'Mara (O'Mara 
) , all over the world, is quite a rare family name. The last name O'Mara is characteristic of Ireland, where it is quite a rare surname, Australia, and New Zealand, where it is a rare surname. Measured by absolute frequency, the name is most common in the United States, Australia, and Ireland.
| VARIANT | COUNTRY |
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| O'Mara | United Kingdom, Australia, Ireland, United States, Canada |
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joseph o'mara Irish singer (1864-1927), IE (b. 1864) |
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| james o'mara Irish politician (1817-1899), IE (b. 1817) |
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james o'mara Irish politician and businessman, IE (b. 1873) |
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| michael j. o'mara politician (b. 1840) |
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ollie o'mara American baseball player, US (b. 1891) |
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| stephen o'mara Irish politician and mayor, IE (b. 1844) |
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| thomas o'mara politician (b. 1847) |
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| stephen m. o'mara Irish businessman and republican politician (b. 1884) |
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kate o'mara English actress, GB (b. 1939) |
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| b. b. o'mara American football player and sports coach (1896–1969) (b. 1896) |
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| phons o'mara (b. 1887) |
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peter o'mara Australian musician, AU (b. 1957) |
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tom o'mara American politician, US (b. 1963) |
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margaret o'mara American historian and academic, US (b. 1970) |
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jason o'mara Irish actor, IE (b. 1972) |
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