Tratnjak families are Croats and they are mostly from Prelog area. In the past century, relatively most of Croatian residents bearing this family name were born in Djurdjevac area and in Cakovec.
Prevalence
About 70 people with faimily name Tratnjak live in Croatia today, in 30 households. There were 70 of them in the middle of the past century, and their number remains constant. They are located in 6 Croatian counties, in 7 cities and 14 other places, mostly in Grabrovnica (10) and Pitomaca (<10) in Djurdjevac area, Dekanovec in Prelog area (<10), Zagreb (<10), and in Belica in Cakovec area (<5).
Outside Croatia
Family name Tratnjak is present in three countries on two continents.
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.