Santhià (Piedmontese: Santhià or Sant'Àgata) is a comune (municipality) in the province of Vercelli in the Italian region Piedmont, located about 50 km northeast of Turin and about 20 km northwest of Vercelli. Santhià is well known for its historic carnival named Carnevale Storico di Santhià since 14th century. The medieval castle of Vettignè is located within the communcal territory. It was built, perhaps over a pre-existing structure, in the 15th century.