Registered as a member of the Hervormde Gemeente Delft (Reformed Church in Delft)

Leeuwenhoek registered as a member of the Hervormde Gemeente Delft (Reformed Church in Delft). In the following years, several of his family members registered, too. There is no record in this archive, beginning in 1657, that his wife Barbara ever registered as a member.

The registration is dated the first two Sundays in September 1658, the 1st and the 8th. Leeuwenhoek's occupation is noted as storekeeper (winkelier) with a residence on the Pooltjesbuurt, a common shortening of the name Hippolytusbuurt.

There were two ways to join, by certificate (attestatie), which transferred membership from another church, or by confession (belijdenis). On the Sunday that Leeuwenhoek joined, he was one of 43 new members by confession.