In Croatia, Kozak families are almost entirely Croats (from Cazma area ), barely Ukrainians (from Bosnian Krajina ). In the past century, relatively most of Croatian residents bearing this family name were born in Bosnian Krajina (Prnjavor area) and in Middle Bosnia (Sarajevo area). In Ratkovac in Bosnian Krajina every fourth inhabitant had the family name Kozak.
Prevalence
About 40 people with faimily name Kozak live in Croatia today, in 17 households. There were 50 of them in the middle of the past century, and their number decreased by 20 percent. They are located in 8 Croatian counties, in 6 cities and 5 other places, mostly in Zagreb (<10), Slavonski Brod (<10), Velika Ludina in Cazma area (<5), Graberje Ivanicko (<5), and in Caginec (<5).
In the sources analysed in the project Acta Croatica so far, the name is mentioned few times, the first time 1917 in source List of Dignitaries, Officials and Public Servants of the Kingdom of Croatia-Slavonia.