Trninić families are mainly Croats and they are mostly from Hrvatska Kostajnica area , often Serbs. In the past century, relatively most of Croatian residents bearing this family name were born in Zagreb and in Hrvatska Kostajnica area. In Gorinja in Cazins Region (Bosnia) every third inhabitant had the family name Trninić.
Prevalence
About 330 people with faimily name Trninić live in Croatia today, in 170 households. There were 440 of them in the middle of the past century, and their number decreased by 20 percent. They are located in almost all Croatian counties, in 35 cities and 38 other places, mostly in Zagreb (80), Rijeka (25), Hrvatska Dubica in Hrvatska Kostajnica area (15), Zadar (15), and in Beli Manastir (15).
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.