Dionysius Godefridus van der Keessel was born in Deventer on 22 September 1738 as the youngest son of the Reformed church minister Dionysius van der Keessel (1700–1755), himself the son of a physician in Dordrecht, and Johanna Wilhelmina Cabeljau (c. 1705–1775). To have a minister or physician in the family background was hardly extraordinary for a Dutch law professor in the eighteenth century. Van der Keessel senior had been rather combative in protecting the unity of the Reformed church. Separatists, pietists, quietists, enthusiasts, and mystics were but a few of the groups he attacked in the lengthy titles of his pamphlets. He published several against the Groningen preacher Wilhelmus Schortinghuis between 1744–1755, and had Schortinghuis’s book on ‘Heartfelt Christianity’ banned by the synod of Overijssel, embarrassing the theological faculty at Groningen, which had already given its approbation. The first son was stillborn but the second son, Samuel Rudolphus van der Keessel (1737–1799), followed in his father’s footsteps and became a minister of the Reformed church in Dordrecht. It seems Dionysius considered theology too, but chose law instead. Van der Keessel’s father and grandfather had both studied at Leiden University.