Marcetelli is a village and comune located in the Province of Rieti within the Lazio region of Italy. It is situated approximately 60 kilometres northeast of Rome and about 25 kilometres southeast of Rieti.
The municipality is characterized by its small size, with a population of 53 residents. Due to this demographic, it holds the distinction of being the least populous municipality in the Lazio region and one of the least populous municipalities in all of Italy.