Castelforte is a town and comune in the province of Latina, in the Lazio region of central Italy.

The medieval town (Castrum Forte, meaning "Strong Castle") was a typical stronghold (probably built to counter the Saracen presence at the Garigliano) with a line of wall and rounded towers; the nearby Suio was defended by a castle.

Castrum Forte's population was increased in 1320 when people from Suio moved here to flee malaria.

People from Castelforte formed two companies which fought alongside Fra' Diavolo in resistance against the French Napoleonic troops in 1798–99.

During the battles of Cassino of World War II, Castelforte, part of the German Gustav Line, was heavily bombed by Allied troops (1943–44).