Isidoor Joseph Polak was married to Rika Pinto. The couple had two children, Frits Leonard Polak and 445726. The family lived at 12 Garstestraat in Winschoten.
Isidoor Joseph Polak was a cashier. He was the treasurer of the Winschoten chapter of the Maatschappij tot Nut der Israëlieten in Nederland. He was also a member of the board of the public reading room. Rika Polak-Pinto chaired the Winschoten chapter of the Dutch association of housewives. She was also a member of the Oranjevereniging. Their son Frits Leonard Polak was a lawyer.
In addition, Jokos files (numbers 54656, 54657) on this family or other family members are at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.The Jokos files reveal that a claim was lodged for compensation for valuables surrendered to the Lippmann-Rosenthal looting bank (L-claim, number 9558/20399).