There have been Jews in the Czech lands for millenia. Unfortunately, throughout those millenia, they have been persecuted to various extents by those who ruled the land. This subject is fascinating and could (and has) fill up volumes of books. It isn’t what I’m posting about today.
From the 17th century forward, when the Catholics dominated the population, Jewish records were kept together with Catholic records in the parish registers. Sometimes they were interspersed; more often, though, they were tacked on to the back in their own group, where you might also find records of orphans and illegitimate children.
I found a specific example of this today in the village of Mniší. Here is the direct link to the beginning of the Jewish births in Mniší, spanning from 1839-1856.