Joseph Slagter was a son of Samuel Slagter and Jeannette Aronius. He married Branca Groen in Amsterdam on 22 October 1924, a daughter of Hartog Groen and Rachel Ark.
City Archive of Amsterdam, archive card of Samuel Slagter and website www.wiewaswie.nl .
In addition, a Jokos file (number 14114) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.