Sant Celoni is a municipality in the comarca of the Vallès Oriental in Catalonia, Spain. It is situated in the valley of the Tordera river between the ranges of Montseny and Montnegre. The main part of the town is on the left bank of the river. The former municipalities of Montnegre and Olzinelles now form part of the municipality of sant Celoni, which has the largest area in the comarca.