Nihonmatsu Domain
Viscount was the 11th (and final) "daimyō" of Nihonmatsu Domain and the 12th hereditary chieftain of the Niwa clan. Nagahiro was the 9th son of Uesugi Narinori of Yonezawa Domain; his mother was a daughter of Matsudaira Yorihiro of Takamatsu Domain. He was married to the eldest daughter of Niwa Nagakuni. Following the defeat of Nihonmatsu Domain during the Boshin War in 1868, Nagakuni was placed under house arrest in Tokyo by the new Meiji government, which also ordered him to retire. Nagakuni formally adopted his son-in-law, Nagahiro who then became "daimyō", with Nihonmatsu reduced to 50,700 "koku" (half of what it had previously held). When the post of "daimyō" was abolished, Nagahiro remained as Imperial governor of Nihonmatsu until the abolition of the han system. Nihonmatsu was incorporated into Fukushima Prefecture. In 1884, with the creation of the "kazoku" peerage system, Nagahiro received the title of "shishaku" (viscount). He died in 1886 and his brother Niwa Nagayasu (Uesugi Narinori's 11th son) became the 13th chieftain of the Niwa clan.