In the Renaissance period, the town fell under the dominion of the Farnese family: it is to them that Valentano owes its fortress (Rocca) and many of its churches. In 1649, when the town of Castro, capital of the Duchy of Castro, was destroyed, Valentano became the natural center of the Castrense region and the custodian of its archives.
In June of 1944, an artillery shell exploded in the "Portonaccio" gate, killing seven civilians who had taken shelter in it. The gate itself is a witness to the tragedy, since one of its stones is missing, but in 2004 a plaque was placed in the Via Trento e Trieste to commemorate all local victims of World War II.