Ilak 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 Bosanian Posavina (Odzak area) and in Trogir. In Gornja Dubica in Bosanian Posavina every tenth inhabitant had the family name Ilak.
Prevalence
About 110 people with faimily name Ilak live in Croatia today, in 50 households. There were 30 of them in the middle of the past century, and their number more than tripled. They are located in 9 Croatian counties, in 10 cities and 9 other places, mostly in Slavonski Brod (25), Zagreb (10), Split (<10), Rovisce in Bjelovar area (<10), and in Lucko (<10).
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.