de Plancy is a French toponym, relating to Plancy-l'Abbaye
Collin de Plancy was born on November 22, 1853 in Plancy, a small town near Troyes in the Champagne region of eastern France, the son of Jacques Auguste Simon Collin de Plancy, a Jesuit priest and prolific writer on the occult whose name is still much more familiar in France than that of his son.