Kos families are almost entirely Croats and they are mostly from Novi Marof area. According to some sources they are from middle Istria, very rarely Serbs. In the past century, relatively most of Croatian residents bearing this family name were born in Zagreb and Varazdin. In Nespeš in Sveti Ivan Zelina every third inhabitant had the family name Kos.
Prevalence
About 4600 people with faimily name Kos live in Croatia today, in 1900 households. There were 4700 of them in the middle of the past century, and their number remains constant. They are located in all Croatian counties, in 87 cities and 518 other places, mostly in Zagreb (895), Varazdin (135), Velika Gorica (115), Rijeka (90), and in Labin (75).
In the sources analysed in the project Acta Croatica so far, the name is mentioned about one hundred times, the first time 1683 in source Catholic Church Parish Records.