Elorrio is a town and a municipality located in the eastern part of the province of Biscay, in the Basque Country, in northern Spain. As of 2017, it has a population of 7,307 inhabitants. It covers an area of 37.20 square kilometers and it has a population density of 193.58 people per square kilometer. It holds the medieval title of Most Loyal and Noble Villa.

The Lordship of Biscay was a region under feudal rule in the region of Biscay in the Iberian Peninsula between c.1040 and 1876, ruled by a political figure known as the Lord of Biscay. One of the Basque señoríos, it was a territory with its own political organization, with its own naval ensign, consulate in Bruges and customs offices in Balmaseda and Urduña, from the 11th century until 1876, when the Juntas Generales were abolished. Since 1379, when John I of Castile became the Lord of Biscay, the lordship was integrated into the Crown of Castile, and eventually the Kingdom of Spain.