Kos, meaning "blackbird", is a Slavic surname. It is very common in Slovenia, Croatia, Poland, Ukraine, and the Czech Republic.
It is the 10th most common surname in Slovenia. [1] Unlike many other Slovene surnames, Kos is found throughout the country, although it's more common in the central and eastern regions than in the west. [1]
It is the third most common surname in the Zagreb County of Croatia. [2]