The village was established by Count Muño (or Nuño Nuñez), who defended the fort at the end of the ninth century against the Arabs. Before that it had been a Celtiberian, Roman and Visigoth fortress.

In 974, Count García Fernández of Castile granted it a charter, the Charter of Castrojeriz, which is considered to be the 1st granted in Castile.

Castrojeriz is an example of Jacobean urbanism, with houses located around the street-route, which is the longest of all on the pilgrimage route. As an important stage in the Camino de Santiago it had several hospitals along this street.