Family name Grennan (Grennan 
) , across the world, is quite a rare last name. The cognomen Grennan is habitual in British Virgin Islands, where it is quite a common surname, Ireland, and Australia, where it is a rare surname. In absolute terms, this name is the most popular in the United States, Ireland, and the United Kingdom.
| VARIANT | COUNTRY |
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| Grennan | Australia, Canada, Ireland, United Kingdom, United States |
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winston grennan Jamaican drummer, creator of one drop reggae beat, flyers beat,, JM (b. 1944) |
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| eamon grennan Irish poet, IE (b. 1941) |
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tom grennan English singer-songwriter, GB (b. 1995) |
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| mike grennan American male curler, US (b. 1950) |
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| david grennan Irish astronomer, IE |
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| sam grennan researcher |
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| penny grennan Labour Party candidate in the 2019 United Kingdom General Election |
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| justin grennan American singer, US |
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| troy grennan researcher (ORCID 0000-0002-8039-6513) |
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| simon grennan researcher |
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| m. adelaide grennan American physician, US |
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| colleen grennan co-founder of Cleopatra's |
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| sean grennan college basketball player (2012–2016) Seton Hall; Fairfield; San Francisco |
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| keith grennan player of American football, US (b. 1984) |
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| winston grennan |
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