Zirdum families are Croats and they are mostly from Bosnian Posavina. According to some sources they are from Posusje (Herzegovina). In the past century, relatively most of Croatian residents bearing this family name were born in Bosanian Posavina (Derventa area) and in Doboj, Bosnia (Doboj area). In places Žeravac and Poljari in Bosanian Posavina every ninth inhabitant had the family name Zirdum.
About 680 people with faimily name Zirdum live in Croatia today, in 250 households. There were 10 of them in the middle of the past century, and their number multiplied. They are located in the most of Croatian counties, in 28 cities and 46 other places, mostly in Zagreb (170), Slavonski Brod (170), Sesvete (65), Cerna in Zupanja area (40), and in Gornja Vrba in Slavonski Brod area (20).
Family name Zirdum is present in 15 countries on four continents.