Alaejos is a municipality located in the province of Valladolid, Castile and León, Spain. According to the 2004 census (INE), the municipality has a population of 1,627 inhabitants. Even though the origins of the town remain uncertain, it is known that it was part of the old province of Toro. Its name around the 12th and 13th century was Falafeios. One theory says that it might have been founded by the Castilian monarchs as a hamlet in the reconquered territories during the Reconquista.
By the mid 14th century, the village had been sold to Medina del Campo by Diego Fernández de Medina. 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. In 1520, the comuneros destroyed a large part of the town. In 1595 it joined Valladolid's Bishopric, even though it kept being part of the Province of Segovia.