Klasan families are Croats and they are mostly from Bosnian Posavina. In the past century, relatively most of Croatian residents bearing this family name were born in Banja Luka Region, Bosnia (Banja Luka area) and in Bosanian Posavina (Bosanska Gradiska area). In Kozara in Bosanian Posavina every fifth inhabitant had the family name Klasan.
About 310 people with faimily name Klasan live in Croatia today, in 120 households. There were 80 of them in the middle of the past century, and their number multiplied. They are located in the most of Croatian counties, in 26 cities and 37 other places, mostly in Zagreb (50), Ivanovac in Osijek area (30), Rijeka (25), Gvozd in Glina area (15), and in Jazavica (15).