Cognomen 洋一郎 (洋一郎 
) , across the world, is a very rare family name. The last name 洋一郎 is characteristic of Eastern Asia, particularly China, where it is an extremely rare surname. More prevalently, 洋一郎 is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| 洋一郎 | China |
| 亀山 洋一郎 Japanese dentist, JP (b. 1936) |
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| 古瀬 洋一郎 Japanese businessman, JP (b. 1941) |
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| あおい 洋一郎 Japanese actor, JP (b. 1963) |
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| 三上 洋一郎 JP (b. 1998) |
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