In Croatia, Kosjek families are Croats (from Bosnian Posavina ). In the past century, relatively most of Croatian residents bearing this family name were born in Zagreb and in Bosanian Posavina (Banovici area).
Prevalence
About 20 people with faimily name Kosjek live in Croatia today, in 6 households. There were 0 of them in the middle of the past century, and their number multiplied. They are located in four Croatian cities only: in Zagreb (15), Bukovcak (<10), Rijeka (<5), and in Rovinj (<5).
In the sources analysed in the project Acta Croatica so far, the name is mentioned over twenty times, the first time 1906 in source Yearbook and Directory of Literary Society of St. Jerome 1906.