Medio Cudeyo is a municipality in the Trasmiera region, in the autonomous community of Cantabria (Spain). It is about 15 kilometers from Santander, the capital of the community. With an area of 26.78 km², it borders the municipalities of Entrambasaguas (to the east), Liérganes and Riotuerto (to the south) and Villaescusa (to the west), and the Miera, Cubón and Pámanes rivers flow through its territories.

Integrated into the Trasmiera region, the capital of the municipality, Valdecilla, is located 16 kilometers from Santander. The municipal area is crossed by the Cantábrico Highway (A-8) and by the national highway N-634, between kilometer points 199 and 202, as well as by the S-10 highway, which allows access to Santander, the national N-635, a conventional alternative to the previous one, the regional highway CA-161, which connects with Riotuerto, and other local roads that allow communication with Liérganes, Marina de Cudeyo and with Peña Cabarga.

The relief of the municipality is defined by the presence of the Miera River on the eastern limit, numerous meadows and low mountains in the central and northern area up to the San Salvador estuary, which acts as a limit to the northwest, and a more mountainous area to the southwest. where the Peña Cabarga Massif stands out, which rises to 569 meters.