In 1774, Kornmann married Catherine Marie Foesch, a young Swiss heiress, who bore him two children.
Furthermore, Madame Kornmann, who did not hesitate to be seen with him in a scandalous way, threatened to demand a separation from her husband (as divorce did not yet exist).
Thus, on the night of 3–4 August 1781, his wife was taken to Douai, a disciplinary institution on the Rue de Bellefond that housed "lost" and mad women.
Once freed, she tried unsuccessfully to obtain a legal separation from her husband, arguing that her scandalous detention justified it.
Kornmann and his lawyer Bergasse were ordered to pay him damages but public opinion remained largely in their favour.