Klaas getrouwd Jantje Hendriks Pijlman on 17 apr 1757 (religious) in Steenwijkerwold. Jantje (dochter van Hendrik Geerts Pijlman en Kunnigjen Jans Hollander) is geboren in 1732 in Kalenberg-IJsselham; is gestorven on 19 apr 1818 in Luinjeberd, Aengwirden, Friesland, Netherlands. [Gezinsblad]

1. Hendrik Klazes Venema is geboren on 12 nov 1758 in Kalenberg-IJsselham.
2. Kunnigje Klazes de Groot is geboren on 30 aug 1760 in Kalenberg-IJsselham; is gestorven on 19 dec 1843 in Aengwirden, Friesland, Nederland.
3. Margjen Klazes de Groot is geboren in jul 1762; is gedoopt on 17 okt 1762 in Oudehaske, Haskerland, Friesland, Netherlands; is gestorven on 3 jan 1845 in Tjalleberd; AEngwirden.
4. Jan klazes de Groot is geboren in in Gersloot, Aengwirden, Friesland, Netherlands; is gedoopt on 14 okt 1764 in Gersloot, Aengwirden, Friesland, Netherlands; is gestorven on 8 sep 1826 in Sneek.
5. Berend Klazes de Groot is geboren in 1769 in Kalenberg-IJsselham; is gestorven on 7 dec 1847 in Opsterland.
6. Folken Klazes de Groot is geboren on 4 dec 1778 in Oudehaske, Haskerland, Friesland, Netherlands.