Alaejos is a municipality located in the province of Valladolid, Castile and León, Spain.

One theory says that it might have been founded by the Castilian monarchs as a hamlet in the reconquered territories during the Reconquista.

It was a jurisdictional dominion by the Bishop of Ávila, Alfonso de Fonseca, until the 19th century.

During the 15th century, Doña Juana de Portugal (Enrique IV's wife) was imprisoned in the castle of Alaejos.

By year 1785, the Royal Economical Society of Charity (Real Sociedad Caritativo Económica) was founded in the town as a part of the spirit of the Age of Enlightenment, which promoted several very advanced economic, social and educational activities for the childhood and the youth of the town.