Cognomen Klaj (Klaj 
, Клай 
) , all around the world, is a rare family name. The surname Klaj is habitual in Hungary, where it is a rare surname, Croatia, and Ukraine, where it is a very rare surname. Measured by absolute frequency, it most frequently occurs in Hungary, Croatia, and Germany. Very seldom, Klaj is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Klaj | Germany, Croatia, Slovenia, India, Hungary |
| Клай | Ukraine, Russia, Kazakhstan |
| johann klaj German poet, DE (b. 1616) |
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| sándor klaj Hungarian miner and mineral collector (b. 1948) |
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