Niwa clan
was a feudal domain under the Tokugawa shogunate of Edo period Japan, located in southern Mutsu Province. It was centered on Nihonmatsu Castle in what is now the city of Nihonmatsu, Fukushima, and its territory included all of Nihonmatsu, Motomiya, Ōtama and most of the present-day city of Kōriyama. For most of its history it was ruled by the Niwa clan. The Nihonmatsu Domain was also the scene of a major battle of the Boshin War of the Meiji Restoration.