In Croatia, Olaj families are generally Croats (from Djurdjevac area ), very rarely Serbs, and . In the past century, relatively most of Croatian residents bearing this family name were born in Pula and Virovitica.
Prevalence
About 20 people with faimily name Olaj live in Croatia today, in 11 households. There were 10 of them in the middle of the past century, and their number doubled. They are only located in in 6 Croatian cities and two other places, mostly in Pula (<5), Varazdin (<5), Vukovar (<5), Novigrad Podravski in Djurdjevac area (<5), and in Osijek (<5).
In the sources analysed in the project Acta Croatica so far, the name is mentioned few times, the first time 1906 in source Yearbook and Directory of Literary Society of St. Jerome 1906.