Jacob Jongejansz Posch was born 17 July 1746 in Hoogkarspel, North Holland, Netherlands to Jongejan Posch (c1712-1795) and Antje Ham (1714-1746) and died 10 February 1833 Hoogkarspel, North Holland, Netherlands of unspecified causes. He married Neeltje Palenstijn (1740-1811) 18 March 1770 in Andijk, North Holland, Netherlands.
Children
| Name | Birth | Death | Joined with |
| Jongejan Posch (1770-1843) | 2 December 1770 Hoogkarspel, North Holland, Netherlands | 21 February 1843 Hoogkarspel, North Holland, Netherlands | Neeltje Houten (1766-1810) Neeltje Kok (1794-1871) |
| Antje Posch (1773-1837) | |||
| Klaas Posch (1780-1780) | |||
Siblings
| Name | Birth | Death | Joined with |
| Barber Posch (1737-1791) | 17 January 1737 Hoogkarspel, North Holland, Netherlands | 2 May 1791 Lutjebroek, North Holland, Netherlands | Arien Koomen (1739-1812) |
| Klaas Jongejansz (1738-1738) | |||
| Klaas Jongejansz (1739-1739) | |||
| Aaltje Posch (1741-) | |||
| Jacob Posch (1746-1833) | 17 July 1746 Hoogkarspel, North Holland, Netherlands | 10 February 1833 Hoogkarspel, North Holland, Netherlands | Neeltje Palenstijn (1740-1811) |
| Name | Birth | Death | Joined with |
| Pieter Posch (1774-bef1807) | |||
| Claas Jongejansz (1775-) | |||
| Jacob Jongejansz (1776-) | |||
| Geertje Jongejans (1778-) | |||
| Crelis Jongejansz (1782-) | |||
| Geertje Posch (1782-1810) | |||