The town of Castelnuovo Parano was formed in the Middle Ages around the castle on Mount Parano that the abbot Desiderio of Montecassino, the future Pope Victor III, built in 1059 to defend the possessions from the continuous attacks by Traetto (Minturno) and Ausonia.
For a long time it marked the border between the territories of the Abbey of Monte Cassino and the Duchy of Gaeta and Castelnuovo remained under the jurisdiction of Cassino, except for some periods when it was occupied by Braccio da Montone, by the counts of Spigno and D ‘Aquino. In 1699 it was incorporated into the Traetto duchy and in 1806 became part of the Bourbon Kingdom.
During the Second World War it suffered heavy bombing, finding itself along the Gustav Line, the German defensive front. After the war the town experienced high emigration.