In Croatia, Schmitz families are generally Croats (from Donji Miholjac area ), very rarely Germans.
Prevalence
About 10 people with faimily name Schmitz live in Croatia today, in 8 households. There were 0 of them in the middle of the past century, and their number multiplied. They are located and two other Croatian places, mostly in Zagreb (<5), Hercegovac in Garesnica area (<5), Karlovac (<5), Valpovo (<5), and in Sveti Ivan Zelina (<5).
Outside Croatia
Family name Schmitz is present in 94 countries worldwide. The family name "Schmitz " is used by some 90000 people in Germany , about 30000 in the United States , and some 20000 people in Brazil. "Schmidtz " is used by some 70 people in the United States , about 50 in Canada , and small number of people in Germany.
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.