On 4 Jun 1825 when Klaas Geerts was 36, he first married Willemtje Hindriks Niemeijer, daughter of Hindrik Willems Niemeijer (ca Apr 1758-3 Jun 1843) & Anke Jans Niemeijer (ca Feb 1763-17 May 1821), in Vlagtwedde, Groningen.538 Born ca 21 Mar 1794 in Vlagtwedde, Groningen.538 Willemtje Hindriks was baptized in Ter Apel, Groningen, on 21 Mar 1794. Willemtje Hindriks died in Ter Apel, Groningen on 30 Apr 1830.

On 20 Jan 1832 when Klaas Geerts was 43, he second married Harmke Harms Kuiper (62776) , daughter of Harm Harms Kuiper (61901) (ca Dec 1768-18 Feb 1808) & Albertje Menses (54655) (ca 1772-7 Jan 1826), in Vlagtwedde, Groningen.538 Born on 12 May 1802 in Ter Apel (Vlagtwedde), Groningen. Harmke Harms was baptized in Ter Apel (Vlagtwedde), Groningen, on 16 May 1801. Harmke Harms died in Ter Apel (Vlagtwedde), Groningen, on 11 Jul 1835; she was 33.