Slonjšak families are Croats and they are mostly from Pregrada area. In the past century, relatively most of Croatian residents bearing this family name were born in Zagreb and in Pregrada area.
Prevalence
About 60 people with faimily name Slonjšak live in Croatia today, in 20 households. There were 30 of them in the middle of the past century, and their number doubled. They are located in four Croatian counties and 8 other places, mostly in Zagreb (30), Stipernica (15), Velika Mlaka (<10), Donji Zbilj in Pregrada area (<10), and in Strmec in Samobor area (<5).
Outside Croatia
Family name Slonjšak is present in this form only in Croatia.
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.