Kupsjak families are Croats and they are mostly from Cazma. In the past century, relatively most of Croatian residents bearing this family name were born in Cazma and Bjelovar. In Vagovina in Cazma every ninth inhabitant had the family name Kupsjak.
Prevalence
About 70 people with faimily name Kupsjak live in Croatia today, in 30 households. There were 70 of them in the middle of the past century, and their number remains constant. They are located in 7 Croatian counties, in 8 cities and 11 other places, mostly in Gornji Draganec (30), Vagovina (15), Cazma (<10), Bjelovar (<10), and in Milasevac (<5).
In the sources analysed in the project Acta Croatica so far, the name is mentioned few times, the first time 2007 in source Encyclopaedia of Croatian Surnames.