Illano is a municipality in the autonomous community of Asturias in northern Spain. It is situated in the western part of the region, within the comarca of Eo-Navia, an area of inland valleys and hills near the border with Galicia.
The municipality is bordered on the north by Boal, on the south by San Martín de Oscos, on the east by Boal, Villayón and Allande, and on the west by Villanueva de Oscos and Castropol. These neighbouring councils place Illano in a sparsely populated rural district of western Asturias.
Illano is one of the smaller and less densely settled municipalities of Asturias, with its population distributed among a number of rural parishes and villages rather than concentrated in a single large town. Its territory is characterised by the mountainous terrain typical of the region's interior.