Niwa clan
is a Japanese castle located in what is now the city of Nihonmatsu, northern Fukushima Prefecture, Japan. Throughout most of the Edo period, Nihonmatsu Castle was home to the Niwa clan, "daimyō" of Nihonmatsu Domain. The castle was also known as or . The castle is one of the 100 Fine Castles of Japan, and in 2007 was designated a National Historic Site. The castle grounds are also a noted venue for viewing sakura in spring.