Cvrtnjak families are Croats and they are mostly from Varazdin area. In the past century, relatively most of Croatian residents bearing this family name were born in Varazdin area and in Varazdin. In Martinkovec in Varazdinske Toplice every ninth inhabitant had the family name Cvrtnjak.
Prevalence
About 100 people with faimily name Cvrtnjak live in Croatia today, in 40 households. There were 50 of them in the middle of the past century, and their number doubled. They are located and 9 other Croatian places, mostly in Semovec in Varazdin area (15), Varazdin (10), Zapresic (10), Trnovec in Varazdin area (<10), and in Orehovica in Cakovec area (<10).
Outside Croatia
Family name Cvrtnjak 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.