Joseph Koekoek was a son of Levie Koekoek and Bernice Tokki. He married Ester Hakker on 15 June 1938 in Den Haag, a daughter of Salomon Hakker and Grietje Porets.

The couple had no children.

Municipal Archive of Den Haag, family registration card of Joseph Koekoek and Civil Registry of Den Haag, certificate of death nr. C690 dated 24 February 1951.