San Costanzo is a comune, or municipality, situated in the Province of Pesaro e Urbino within the Marche region of central Italy. It is located approximately 40 kilometres northwest of the city of Ancona and about 20 kilometres southeast of Pesaro.
The town serves as a local administrative center in its respective province. Its geographical position places it within the coastal vicinity of the Adriatic Sea, characterized by its proximity to major regional hubs like Pesaro and Ancona.