松平定信
was a feudal domain under the Tokugawa shogunate of Edo period Japan, located in southern Mutsu Province. It was centered on Komine Castle in what is now the city of Shirakawa, Fukushima. Its most famous ruler was Matsudaira Sadanobu, the architect of the Kansei Reforms. It was also the scene of one of the battles of the Boshin War of the Meiji restoration.