Castrillo de la Valduerna is a municipality in the province of León, within the autonomous community of Castile and León, Spain. It lies in the northwestern part of the country, in the region traditionally known as the Valduerna, after which the municipality takes part of its name.
The municipality is small and rural. According to the 2025 census conducted by Spain's National Statistics Institute (INE), it had a population of 136 inhabitants. That figure reflects the pattern of low and declining population common to many villages in this part of inland northern Spain.
As a municipality, Castrillo de la Valduerna is the basic unit of local administration in Spain, with its own local government. Beyond its administrative status, location in the province of León, and its recorded population, the available reference material provides no further details about its history, economy, or landmarks.