Born November 14, 1653 to Jean de La Croix de Chevrières de Saint-Vallier and Marie de Sayve, Jean-Baptiste was part of the La Croix family, known to be ranked among the best in Dauphiné with prestigious posts such as country noblemen, officers, magistrates and ambassadors. Jean-Baptiste's father was a Grenoble magistrate and worked for the diplomatic services and his grandfather was a lawyer and poet, then a judge at the Parliament of Grenoble. The La Croixs owned a large amount of land including the castle of Saint-Vallier in the Rhone, which previously belonged to King Henry II's mistress, Diane de Poitiers.