Castel di Casio is a comune located in the Metropolitan City of Bologna within the Emilia-Romagna region of Italy. It is situated in the Bolognese Apennines, approximately 60 kilometres (37 mi) southwest of the city of Bologna.
The municipality is positioned in the valley of the Limentra stream. Geographically, it lies between Lake Suviana and the confluence where the Limentra meets the Reno river.