In Croatia, Reiss families are Croats (from Zagreb ).
Prevalence
About 10 people with faimily name Reiss live in Croatia today, in four households only. There were 10 of them in the middle of the past century, and their number remains constant. They are located in two Croatian cities only, in Zagreb (<5) and Kutina (<5).
Outside Croatia
Family name Reiss (including: Reiß , Reyss ) is present in 66 countries worldwide. The family name "Reiss " is used by some 10000 people in the United States , about 8000 in Germany , and some 1000 people in France.
In the sources analysed in the project Acta Croatica so far, the name is mentioned over ten times, the first time 1902 in source Hartmann's General List of Apartments in Zagreb.