Aizu Domain

Aizu (会津)
Region
Tsuruga Castle, located in Aizuwakamatsu
Country	Japan
Prefecture	Fukushima
Area	5,420.69 km2 (2,093 sq mi)
Population	291,838 (1 October 2010)
Density	54/km2 (140/sq mi)
Aizu comprises the western third of Fukushima Prefecture

Aizu (会津, Aizu^?) is the westernmost of the three regions of Fukushima Prefecture in Japan, the other two regions being Nakadōri in the central area of the prefecture and Hamadōri in the east. As of October 1, 2010, it had a population of 291,838. The principal city of the area is Aizuwakamatsu.

During the Edo period, Aizu was a feudal domain known as Aizu Domain (会津藩, Aizu-han^?). It was part of Mutsu Province; the area once was part of Iwase Province in the 8th century and, before the prefectural system, Iwashiro Province. Although never an official province in its own right, Aizu was considered as such de facto, and even today local Japan Rail stations prefix "Aizu-" to names instead of "Iwashiro-", as it was for stations around the center of Fukushima Prefecture.

The daimyo over much of the Edo period was from the Hoshina family. They had been senior retainers of the Takeda family, and in the early 17th century the head of the family, Hoshina Masamitsu, adopted the illegitimate son of the second Tokugawa shogun Hidetada. As a result, the Hoshina family's fortunes rose, with larger and larger fiefs being given to them, until finally they were moved to Aizu, then rated at 240,000 koku, in the mid-17th century. Hoshina Masayuki, the adopted head of the family, rose in prominence while his half-brother Tokugawa Iemitsu was shogun, and later acted as a regent for his successor, the underage fourth shogun Tokugawa Ietsuna. By the end of the 17th century, the Hoshina family was allowed the use of the Tokugawa hollyhock crest and the Matsudaira surname, and from then on was known as the Aizu-Matsudaira clan, with the name Hoshina being used mainly for internal documents.