What's new

Castle Koizumi Castle

This article is in the series Walking the Japanese Castles
Leave a rating
Koizumi Castle (小泉城 Koizumi-jō) is a former flatland castle located in Oizumi (大泉町), Ora-gun, in southeastern Gumma Prefecture. The castle was built in 1489, the first year of the Entoku era (延徳, 1489-1492). Today, only the ruins of the castle (all of the inner moat, part of the outer moat and earthworks) remain, and the area has been developed into Shiro-no-uchi Park (城之内公園).


The castle was built by Ashikaga Shigeuji's son Mochimitsu (later known as Tomioka Naomitsu, 冨岡直光), who lost in the Siege of Yūki (結城合戦) in 1440 and was later given the territory of Ora-gun. It was around this time that it came to be known as Koizumi Castle. The Tomioka clan played an active role under the Koga kubō (古河公方), Uesugi Kenshin (上杉謙信, 1530-1578), and the Late Hōjō. Later, the Koizumi clan formed a new family branch independent of the Tomioka. However, in 1590, when Toyotomi Hideyoshi invaded the Kantō region, the Koizumi were attacked by Asano Nagamasa (浅野長政, 1546-1611), Hideyoshi's brother-in-law; the castle fell and was abandoned.

Between the remaining sotobori (外堀, outer moat of a castle) and uchibori (内堀, inner moat), there are more than a dozen oval stone pillars engraved with Kōshin (庚申) symbols believed to date back to the Edo period when the Kōshin faith, a folk belief with Taoist origins, influenced by Shintō and Buddhism, was flourishing.

The castle consists of a honmaru (本丸, inner enclosure), a ninomaru (二ノ丸, second enclosure) and a sannomaru (三ノ丸, third enclosure). The moats have been renovated and the earthworks still are in good shape; the moat in the photo below is situated on the castle's north side.


Based on the Aerial Photograph Searching Service of the Geospatial Information Authority of Japan. The location of the enclosures is estimated.


Local guide board


Earthworks on the west side of the sannomaru.


The view of the sannomaru from the honmaru.


There is a school on the south side of the sannomaru.


This is the moat surrounding the honmaru.


The honmaru is surrounded by earthwork as well. Incidentally, Oizumi Town is home to a large community of foreign workers. I saw a Japanese-Brazilian family playing football in the park.


Date of visit: 24 November 2013


  • Address: 2-21-11 Shironouchi, Oizumi, Ora District, Gunma 370-0518
  • Access: an 8-minute walk from Tōbu Koizumi Line (東武小泉線) Koizumi-cho Station
    9 kilometres from Kita-Kanto Expressway Ota-Kiryu Interchange via National Route 122
  • Parking: in the park (see the 'P' in the map above)
  • Other sights: Ashikaga Residence
Next article in the series 'Walking the Japanese Castles': Kanayama Castle
Previous article in the series 'Walking the Japanese Castles': Ashikaga Residence
  • Like
Reactions: thomas
About author
Hiroto Uehara
Hiroto is an ordinary Japanese office worker, but his true mission is searching for castles on the weekend.


My wife and I visited the castle in the same year. I remember hearing a lot of Portuguese in the castle park, too. :)

Series table of contents

Iwatsuki Castle Shakujii Castle Oda Castle Tsuchiura Castle Miharu Castle Inohana Castle Setagaya Castle Konodai Castle Usui Castle Sakura Castle Kozukue Castle Masugata Castle Koga Castle Tenjinyama Castle Ogura Castle Sugaya Castle Sugiyama Castle Kogane Castle Kokokuji Castle Nagahama Castle (Izu) Nirayama Castle Hachigata Castle Futagamiyama Castle Edo Castle Kawahara Castle Kageishi Castle Wakasa-Onigajo Castle Tenjinyama Castle (Tottori) Tsuzurao Castle Ueshi Castle Jindaiji Castle Kururi Castle Mariyatsu Castle Narukami Castle Ryozen Castle Kori-Nishiyama Castle Tsutsujigasaki Residence Yogai Castle Kofu Castle Iwadono Castle Hachioji Castle Takiyama Castle Suemori Castle Nagoya Castle Inuyama Castle Kiyosu Castle Tatebayashi Castle Sano Castle Karasawayama Castle Ueda Castle Sanada Residence Sanada Honjo Toishi Castle Katsurao Castle Uchiyama Castle Hiraga Clan Castle Taguchi Castle Tatsuoka Castle Komoro Castle Matsushiro Castle Kajiki Castle Kakuto Castle Hitoyoshi Castle Ichiuji Castle Izaku Castle Chiran Castle Kiyoshiki Castle Kamo Castle Miyakono Castle Obi Castle Shibushi Castle Koyama Castle Mukasa Castle Sadowara Castle Tonokoori Castle Taka Castle Nerima Castle Kawagoe Castle Ashikaga Residence Koizumi Castle Kanayama Castle Shinagawa Battery (Odaiba) Tamba Kameyama Castle Yagi Castle Sonobe Castle Fushimi Castle Yodo Castle Shoryuji Castle Yamazaki Castle Tsukui Castle Katakura Castle Hirayama Castle Site Park Yamanaka Castle Sanuki Castle Sunpu Castle Koyama Castle (Shizuoka) Ryugenzan Castle Sagara Castle Tanaka Castle (Shizuoka) Ishiwaki Castle Hanazawa Castle Mochifune Castle Moriyama Castle (Aichi) Obata Castle (Aichi) Ryusenji Castle Gakuden Castle Komakiyama Castle Iwakura Castle (Aichi) Kano Castle Gifu Castle Kitagata Castle Sone Castle Ōgaki Castle Ōtaki Castle Obata Castle (Ibaraki) Mito Castle Kasama Castle Tanagura Castle Akadate Castle Inawashiro Castle Aizu-Wakamatsu Castle Mukai-Haguroyama Castle

Article information

Hiroto Uehara
Article read time
2 min read
Last update
〒370-0518 群馬県邑楽郡大泉町城之内2丁目21−11

More in Gunma

More from Hiroto Uehara

Top Bottom