Pieter Koster/Molenaar was born 31 January 1727 in Wervershoof, North Holland, Netherlands to Maarten Koster (1699-1773) and Vrouwtje Crelis (-1735) and died 21 November 1809 Hoogkarspel, North Holland, Netherlands of unspecified causes. He married Maartje de Goede (c1730-1788) 29 July 1748 in Westwoud, North Holland, Netherlands. He married Trijntje Molenaar (-) 26 October 1789 in Grootebroek, North Holland, Netherlands.
Children
| Name | Birth | Death | Joined with |
| Vrouwtje Pieters (1751-1751) | |||
| Grietje Pieters (1752-1752) | |||
| Vrouwtje Pieters (1752-1752 | |||
| Vrouwtje Koster (1758-1807) | 10 May 1758 Wijzend, Hoogkarspel, North Holland, Netherlands | 18 September 1807 Hoogkarspel, North Holland, Netherlands | Cornelis Prins (1756-1808) |
| Jan Koster (1760-1821) | 28 December 1760 Wijzend, Hoogkarspel, North Holland, Netherlands | 22 January 1821 Wijzend, Hoogkarspel, North Holland, Netherlands | Aafje Bakker (-1791) Aagje Ootes (1771-1835) |
| Jacob Pietersz (1763-bef1764) | |||
| Jacob Pieters (1764-1764) | |||
| Jacob Pietersz (1765-1765) | |||
| Crelis Pietersz (1766-1767) | |||
| Maarten Pietersz (1769-1769) | |||
| Maarten Koster (1771-1806) | |||
Siblings
| Name | Birth | Death | Joined with |
| Trijntje Koster (1725-1788) | 19 November 1725 Wervershoof, North Holland, Netherlands | 30 December 1788 Wervershoof, North Holland, Netherlands | Cornelis Koopman (1712-1789) |
| Pieter Koster (1727-1809) | 31 January 1727 Wervershoof, North Holland, Netherlands | 21 November 1809 Hoogkarspel, North Holland, Netherlands | Maartje de Goede (c1730-1788) Trijntje Molenaar (-) |
| Cornelis Maartensz (1729-1731 | |||
| Aafje Maartens (1731-1735 | |||
| Cornelis Molenaar (1731-1800) | |||
| Jacob Maartensz (1733-1735) | |||
| Dirk Maartensz (1735-1735) | |||