In Croatia, Terstenjak families are Croats (from Varazdin ). In the past century, relatively most of Croatian residents bearing this family name were born in Varazdin and in Cakovec area.
Prevalence
About 10 people with faimily name Terstenjak live in Croatia today, in five households only. There were 20 of them in the middle of the past century, and their number halved. They are located in two Croatian cities only, in Varazdin (<10) and Crikvenica (<5).
Outside Croatia
Family name Terstenjak is present in 7 countries on two continents. "Terstenyak " is used by small number of people in the United States.
In the sources analysed in the project Acta Croatica so far, the name is mentioned over thirty times, the first time 1902 in source Hartmann's General List of Apartments in Zagreb.