Jacob Zak was a son of Machiel Zak and Judith Olivier. He married 21 March 1900 in Amsterdam Cornelia Pots, a daughter of Simon Pots and Rachel Koopman.
The couple had six children: the at home with their parents living Simon and Elisabeth, Michiel, Rachel, Judith and a son who survived the war, however not his wife Anna Italiaander and both his children.
Jacob himself was born in a family with twelve children. Two of them have died in childhood. The other children all have been killed during the Holocaust.
City Archive of Amsterdam, family registration card of Machiel Zak, archive card of Jacob Zak and www.wiewaswie.nl.