In Croatia, Ondrušek families are Croats (from Sisak ). In the past century, relatively most of Croatian residents bearing this family name were born in Sisak.
Prevalence
About 10 people with faimily name Ondrušek live in Croatia today, in four households only. There were 10 of them in the middle of the past century, and their number remains constant. They are located in three Croatian cities only: in Sisak (<10), Zagreb (<5), and in Rijeka (<5).
In the sources analysed in the project Acta Croatica so far, the name is mentioned over five times, the first time 1902 in source Hartmann's General List of Apartments in Zagreb.