Last name O'Leary (O'Leary 
, או'לירי 
) , in the world, is a common family name. The cognomen O'Leary is habitual in Ireland, where it is a common surname, Guernsey, where it is quite a common surname, and Australia. Measured by absolute frequency, this name is the most popular in Ireland, the United States, and Australia.
| VARIANT | COUNTRY |
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| O'Leary | Australia, Ireland, Canada, United States, United Kingdom |
| או'לירי | Israel |
| arthur o'leary Irish Franciscan preacher and polemical writer (b. 1729) |
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daniel florence o'leary Irish general and aide-de-camp under Simón Bolívar (1801-1854), IE (b. 1801) |
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| narcisa emília o'leary IE (b. 1770) |
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| maura bwee o'leary (b. 1774) |
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| joseph o'leary Irish barrister and legal writer (b. 1792) |
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edward o'leary Irish catholic priest, IE (b. 1845) |
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| joseph o'leary Irish songwriter and journalist (b. 1795) |
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de lacy o'leary British historian, GB (b. 1872) |
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| thomas connor o'leary (1822-1885) (b. 1822) |
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john william o'leary American businessman, US (b. 1875) |
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charley o'leary American baseball player and coach (1875–1941), US (b. 1875) |
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| catherine o'leary Alledged start of the Great Fire of Chicago, IE (b. 1827) |
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henry joseph o'leary Catholic archbishop, CA (b. 1879) |
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| ellen o'leary Irish poet, IE (b. 1831) |
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| henry o'leary Canadian politician, CA (b. 1832) |
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