Ōno Castle was an ancient castle (also known as a Korean-style fortresses in Japan straddling the border of the cities of Ōnojō and Dazaifu, and the town of Umi, Fukuoka Prefecture Japan. Its ruins have been protected as a National Historic Site since 1932, and raised to a Special Historic Site since 1953 with the area under protection expanded in 2012.The name of Ōnojō City comes from this castle; however, approximately 80% of the castle area is within the boundaries of Umi Town.

Over the course of the Yamato period, in the early centuries of the establishment of a Japanese state, a great number of Korean-style fortresses were constructed in Japan. Old fortresses dating to the 8th century and earlier can be found all over western Japan. Many of these sites have been identified with fortresses whose construction, repair, and destruction are described in detail in ancient chronicles such as Nihon Shoki and Shoku Nihongi. According to some interpretations of these texts, these fortresses were built under the guidance of, and at the orders of, various members of the Korean nobility or royalty.