"Jouy" is a direct translation of Latin "gaudium", both meaning "joy". Josas was the ancient name of an archdiaconate of the archbishop of Paris. Although many discoveries in various parts of the town attest to there once having been a Gallo-Roman presence there, the first traces of the construction of a village are of the ninth century. Stimulated by the presence of monks from the abbey of Saint-Germain-des-Prés in Paris, Jouy grew rapidly, but the population was progressively annihilated in the fourteenth century by a number of wars and epidemics. By 1466, there were only three houses left in the village.