It is located in the northeastern part of Alava inside the agricultural flatness known as Plain Of Alava and of Band of Salvatierra.

The municipality is composed by 15 villages of small size, which although grouped administratively in a common municipality, constitute in turn councils, what gives them certain autonomy administrative in topics like the management of the common grounds of every council or village.

The municipality of San Millán takes it as a historical precedent Brotherhood of Eguilaz, which was grouping most of the Towns of the current municipality and which sinks his roots in the Middle Age. Them fraternity of Alava was groups of villages that were signing agreements on his defense and mutual protection during the stormy ones times of the partisan wars in the second half of the XIV.th century They usually took the name of the most important population who was forming the above mentioned brotherhood. There are known the ordinances of the brotherhood that date of 1360, although it is known that this previous age. The Brotherhood of Eguilaz was one of 14 fraternity that gathered together to form the province of Alava.

In the quarter of Barria, belonging to Narvaja there is Cistercian monastery of San Bernardo of Barria, who dates of XIIth century, although the current building is of the XVth century. At present monastery has been re-turned into hostel of the Statutory Delegation of Alava and receives young Town in summer camps.
Very close to Eguilaz there was discovered in 1832 a dolmen, which was excavated in 1965, remaining open the south part of the tumulus. dolmen of Eguilaz or of Aizkomendi is one of the prehistoric remains better preserved than the Basque Country. The dolmen is perfectly visible from the divided highway N-1 in direction of Vitoria.
In September, 2005 they began, directed by a team of archaeologists of the Basque Public University (UPV-EHU), some excavations in the deposit of Zornostegui (Luzuriaga), a village medieval founded does approximately thousand years and that was left in period bajomedieval, approximately 600 years ago.

Holidays and traditions
Holiday of San Román: there celebrates last weekend of May in the Ist populate of San Román of San Millán (as it would be necessary to wait). More crowded management holidays of the municipality are them . They usually celebrate motorbike - cross competitions.

Pilgrimage of Guipuzuri: it is celebrated on July 2 in the Saint's chapel Elizabeth de Guipuzuri in the precincts of the Ist populate of Adana.

Most of the Towns of San Millán celebrates his respective ones management holidays. (ftes. to see the links)

Nuclei of San Millan / Donemiliaga: Adana, Aspuru/Axpuru, was Sweeping, Bikuña/Vicuña, Durruma/San Román of San Millán, Eguilaz/Egilatz, Galarreta, Luzuriaga, Mezkia, Munain, Narvaja, Okariz, Ordoñana/Erdoñana, San Millán/Donemiliaga, Txintxetru, Ullibarri-Jauregi/Uribarri-Jauregi, Zuazo of San Millan/Zuhatzu Donemiliaga