Jacob Polak was a son of Philip Polak and Catharina de Jong. He married Rachel Stork in Amsterdam on 6 November 1907, a daughter of Levie Emanuel Stork and Anna van Baren. The couple had four children, of whom three have survived the Holocaust. Only his daughter Elisabeth has been killed during the Shoah too.
City Archive of Amsterdam, archive card of Jacob Polak and website www.wiewaswie.nl.