The County of Clermont-en-Argonne was a feudal domain in the Holy Roman Empire during the Middle Ages and in the Kingdom of France during the early modern period. It was centred on the fortified hilltop town of Clermont-en-Argonne in the diocese of Verdun. The term Clermontois can refer both to the region around Clermont and to the people of the town and region.
Clermont-en-Argonne with its dependencies (that is, the surrounding countryside) was given to the bishop of Verdun in 719 by Charles Martel, duke of the Franks. The county of Clermont-en-Argonne originated in the middle of the tenth century as a benefice for the advocatus (lay defender) of the diocese of Verdun.
In 1094, Clermont-en-Argonne was seized by a certain Odo and then recaptured by the bishop, Richer. In 1110, the count, Dudo, was accused of having "insulted" the bishop and was besieged in Clermont by the Emperor Henry V. Thereafter, throughout the twelfth century, the town was disputed between the bishops and the counts of Bar, several times being besieged and even burnt. After the counts gained the military advantage, they agreed to do homage to the bishop in return for Clermont. Once in legal possession of the town, the counts of Bar built strong fortifications. In the thirteenth century, Count Henry II built a fortress on the Plateau de Sainte-Anne outside Clermont. The inhabitants of the fortified plateau were enfranchised by Count Theobald II in 1246 and those of the town itself by Duke Henry IV in 1339, the counts of Bar having by then been raised to the status of dukes. In 1354, Henry IV's widow, the Countess Yolande, ruling on behalf of her young son Robert, established a mint at Clermont-en-Argonne. After 1431, the counts of Bar were also Dukes of Lorraine.