Trtinjak 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.
Prevalence
About 100 people with faimily name Trtinjak live in Croatia today, in 40 households. There were 70 of them in the middle of the past century, and their number increased by 30 percent. They are located in two Croatian counties, threee cities and 6 other places, mostly in Turcin in Varazdin area (30), Varazdin (25), in Varazdin Breg (20) and Sracinec (15) in Varazdin area, and in Zagreb (<10).
Outside Croatia
Family name Trtinjak 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.