Castropol is a municipality in Asturias, Spain. The name also refers to a parish within the municipality and to a town within that parish.
The municipality is located in the western part of Asturias, in northern Spain. It lies on the coast, near the estuary of the Eo River, which forms the boundary between Asturias and the neighbouring region of Galicia.
Castropol is one of the municipalities that make up the comarca of Eo-Navia, the westernmost of Asturias's administrative districts. The area is known for its coastal and estuarine landscapes, where the Eo River meets the Bay of Biscay.