Meijer van der Horst was a son of Karel van der Horst and Reintje Turksma. He married 23 May 1934 in Amsterdam to Rosa Ketellapper, a daughter of Abraham Ketellapper and Vrouwtje Kloot. the couple had two children.
Also Rosa's unmarried uncle lived in with the van der Horst family, Nathan Ketellapp…
In addition, a Jokos file (number 6932) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.