Košir 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 Cakovec and in Cakovec area.
Prevalence
About 170 people with faimily name Košir live in Croatia today, in 70 households. There were 70 of them in the middle of the past century, and their number more than doubled. They are located in the most of Croatian counties, in 15 cities and 17 other places, mostly in Nedelisce in Cakovec area (20), Varazdin (20), Zagreb (15), Cakovec (15), and in Pula (10).
In the sources analysed in the project Acta Croatica so far, the name is mentioned over twenty times, the first time 1906 in source Yearbook and Directory of Literary Society of St. Jerome 1906.