Casasola de Arión is a village and municipality in the province of Valladolid, within the autonomous community of Castile and León, Spain. It is located in the northern part of the Iberian Peninsula, in the region historically known as Old Castile.
The municipality covers an area of 27.65 square kilometres (10.68 square miles). As of 2011, its population stood at 314 people, making it a small and sparsely populated rural settlement typical of the region.