Last name 大井 (大井 
, Оои 
, Ōi) , all around the world, is a very rare cognomen. The last name 大井 is habitual in China, where it is an extremely rare surname, and Russia. More prevalently, 大井 is the forename as well as the last name.
| 大井浩二 Japanese teacher, JP (b. 1933) |
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| 大井さちこ Japanese printmaker, JP (b. 1962) |
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| 大井健太郎 Japanese association football player, JP (b. 1984) |
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