In Croatia, Kajs families are generally Croats (from Zagreb ), very rarely Serbs. In the past century, relatively most of Croatian residents bearing this family name were born in Zagreb and in Klanjec area.
Prevalence
About 10 people with faimily name Kajs live in Croatia today, in five households only. There were 0 of them in the middle of the past century, and their number multiplied. They are located in two Croatian counties, in one city and another small place , mostly in Zagreb (15) and Marija Gorica in Zapresic area (<5).