Castrillo de Villavega is a municipality in the province of Palencia, in the autonomous community of Castile and León, Spain. It lies in the northern part of the country, within the broad plains of the Tierra de Campos region that characterises much of Palencia's countryside.
The municipality is small and rural in character. According to the 2004 census carried out by Spain's National Statistics Institute (INE), it had a population of 255 inhabitants. Like many villages in this part of Castile and León, it is a compact settlement surrounded by agricultural land.
Its administrative status as a municipality places it among the many small local authorities that make up the province of Palencia, whose capital city of the same name lies to the south. The village's name combines the common Castilian place-element "Castrillo," meaning a small fort or hillfort, with the distinguishing suffix "de Villavega."