Perched at the top of the town, the Lauragais Museum is housed in the town’s former prison. Every year a new exhibition takes place there.
The Musée du Lauragais was built when Catherine de Médicis, Countess of Lauragais, made Castelnaudary a Seneschalee with the King’s consent. A court of civil and criminal justice, called “Présidial”, was then built right next to the castle. It was completed in 1585. In 1623, Louis XIII had the castle of Castelnaudary demolished, but the court itself was in operation until 1926. His presence made it possible for many Toulouse judges and lawyers to settle in the town; very beautiful mansions still bear witness to this.