In Croatia, Sišak families are Croats (from Rijeka ). In the past century, relatively most of Croatian residents bearing this family name were born in Rijeka.
Prevalence
Only a few people with faimily name Sišak live in Croatia today, in two households only. There were 0 of them in the middle of the past century, and their number multiplied. They are located in two Croatian cities only, in Rijeka (<10) and Zagreb (<5).
In the sources analysed in the project Acta Croatica so far, the name is mentioned over five times, the first time 1683 in source Catholic Church Parish Records.