Family name Kostelnik (Kostelnik 
) , around the world, is quite a rare last name. The family name Kostelnik is characteristic of Slovakia, where it is quite a rare surname, Czechia, and Croatia, where it is a rare surname. Not in comparison with a country's population, this name is the most popular in the United States, Czechia, and Slovakia. Much less frequently, Kostelnik is the forename as well as the last name.
| VARIANT | COUNTRY |
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| Kostelnik | Slovakia, Czechia, United States, Germany, Poland |
Kostelník, Костелник, Костельник, and Костельнік
| josif kostelnik (b. 1903) |
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michael c. kostelnik United States general, US |
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| ron kostelnik American football player (1940-1993), US (b. 1940) |
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| branko kostelnik (b. 1961) |
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| kevin michael kostelnik environmental researcher |
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| adam kostelnik researcher |
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