Geertje Jans was born 1713 to Jan Jacobsz and Aacht Cornelis and died 17 February 1752 Andijk, North Holland, Netherlands of fever. She married Pieter Sijm (1711-1752) 28 January 1739 in Wervershoof, North Holland, Netherlands.
Note that there are three hypotheses for Geertje's parents: Jan Jacobsz & Aacht Cornelis, Jan Jacobsz & Greetje Pieters, Jan Tiet & Immetje Dekker. Nico Sijm claims Pieter is Geertje's first cousin.
Children
| Name | Birth | Death | Joined with |
| Jan Sijm (1739-1822) | 17 July 1739 Wervershoof, North Holland, Netherlands | 21 January 1822 Andijk, North Holland, Netherlands | Antje Knuijsen (1737-1825) |
| Anna Sijm (1742-?) | |||
| Sijmen Sijm (1744-1804) | 19 April 1744 Onderdijk, North Holland, Netherlands | 5 November 1804 Bangert, Andijk, North Holland, Netherlands | Neeltje Akkerman (c1743-1808) |
| Cornelis Sijm (1746-1809) | 3 August 1746 Onderdijk, North Holland, Netherlands | 14 February 1809 Blokker, North Holland, Netherlands | Meinouwtje Buurman (1749-1825) |
| Adrianus Sijm (1750-1762) | |||
Footnotes (including sources)
| ‡ General |