The origin of surname Castellanos is Galicia, northwestern Spain.

Although people were originally known only by their first names, it became necessary to adopt a second name to identify due to population growth.

The most common type of family name found in the region was the surname that derives from the name of the father.
During the Middle Ages the patronymic system adopted for surnames.
Then in Italy during the Christian era, people often gave as a second name to their children the names of saints or biblical figures.
The nicknames as surnames usually reflected the physical characteristics of the first member of the lineage.
The local names describe a region or place where they lived the first members of the lineage.
Many Spanish surnames are influenced Germanic and Arabic words or names of places because of the occupation of both cultures in a period of time.
The surname Castellanos occupational in origin and described a person who worked in a castle.

Some variations of this surname are: Castellanos, Castilian, and others.