Castrillo de Don Juan is a municipality in the province of Palencia, within the autonomous community of Castile and León, Spain. It is located in the northern part of the country, in a region characterised by the flat plains and agricultural landscapes of the Castilian meseta.
The municipality is small, with a recorded population of 305 inhabitants according to the 2004 census conducted by Spain's National Statistics Institute (INE). Like many rural settlements in the province of Palencia, it is a compact village whose demographic profile reflects the broader pattern of depopulation seen across much of inland Castile and León.
Its administrative status as a municipality means it has its own local government, or ayuntamiento, which manages the basic services for the resident population. The town lies within the comarca, or district, surrounding the provincial capital of Palencia, though specific details about its economy, history, and landmarks are not documented in the available source material.