若狭国
Ōi is part of ancient Wakasa Province. During the Edo period, the area was part of the holdings of Obama Domain. Following the Meiji restoration, it was organised into part of Ōi District in Fukui Prefecture. With the establishment of the modern municipalities system on April 1, 1889, the villages of Saburi, Ōshima, and Hongō were established. These villages merged to form the town of Ōi on January 15, 1955. On March 3, 2006 the village of Natashō, from Onyū District, was merged into Ōi, which is since written with "hiragana" instead of "kanji". Before the merger the town was written 大飯町.