Knjaz families are Croats and they are mostly from Zapresic area. In the past century, relatively most of Croatian residents bearing this family name were born in Zagreb and in Zapresic area.
Prevalence
About 100 people with faimily name Knjaz live in Croatia today, in 50 households. There were 100 of them in the middle of the past century, and their number remains constant. They are only located in in 6 Croatian cities and 8 other places, mostly in Zagreb (45), Jakovlje in Zapresic area (30), Osijek (<10), Kraljev Vrh in Zapresic area (<10), and in Visnjevac (<5).
Outside Croatia
Family name Knjaz (including: Knyaz , Kniaz and Knyazh ) is present in 29 countries worldwide. "Kniaz " is used by some 500 people in Poland , about 200 in the United States , and small number of people in Georgia.
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.