Surname Diffley (Diffley 
) , in the entire world, is a rare last name. The cognomen Diffley is habitual in Ireland, where it is quite a rare surname, the United States, where it is a rare surname, and New Zealand. In absolute terms, it is the most numerous in the United States, Ireland, and the United Kingdom.
| VARIANT | COUNTRY |
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| Diffley | United Kingdom, Australia, Ireland, United States, Canada |
| john francis xavier diffley molecular biologist, US (b. 1958) |
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| john diffley American soccer player and coach, US (b. 1967) |
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| joe diffley college basketball player (1967–1969) Santa Clara |
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