Founded in August 1841 during the Edo period, Kodokan was the domain school of the Mito Clan, and it was the largest of its kind in Japan at the time.

Kodokan was founded to educate samurai in both civil and military skills. It covered a wide range of subjects, including Confucianism, Kokugaku (National Studies), martial arts, medicine, astronomy, and Dutch studies. In a way, it functioned as a comprehensive university for its time.

Currently, the grounds of Kodokan are home to around 800 plum trees of approximately 60 varieties. Along with Kairakuen Garden, it is renowned as one of the top plum blossom viewing spots.

Furthermore, Kodokan is designated as a Special National Historic Site, with three of its buildings—the main gate, main hall, and Shizendo Hall—have been designated as Important Cultural Properties.