Hillel Baum was born as Herbert Siegmund Baum in Alzey in September 1928. He was the first child of Klara and Ludwig Baum.

His sister Senta was born in December 1933.

Alzey was a small town in Rhineland-Palatinate and had about 9,000 inhabitants at that time. About 200 of them were Jews. The Jewish community had its own synagogue and employed a rabbi.