Kosir families are Croats and they are mostly from Ludbreg area. In the past century, relatively most of Croatian residents bearing this family name were born in Herzegovina (Siroki Brijeg area) and in Zagreb.
Prevalence
About 120 people with faimily name Kosir live in Croatia today, in 40 households. There were 120 of them in the middle of the past century, and their number remains constant. They are located in the most of Croatian counties, in 12 cities and 14 other places, mostly in Zagreb (45), Bedekovcina in Lepoglava area (10), Belica in Cakovec area (10), Zabok (<10), and in Rijeka (<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.