Ōta Town was created within Nitta District, Gunma Prefecture on April 1, 1889 with the creation of the modern municipalities system after the Meiji Restoration. On April 1, 1940, Ōta merged with the villages of Kuai and Sawano from Nitta District, and with the village of Niragawa from Yamada District. On November 1, 1943, Ōta absorbed the village of Shimanogō, also from Nitta District. Ōta was elevated to city status on May 3, 1948. The city expanded on April 1, 1957, by annexing the village of Kyodo (from Nitta District), and the village of Kyūhaku (from Yamada District), and by annexing parts of the village of Yabakawa (Yamada District) on July 1, 1960. On April 1, 1963, Ōta absorbed the village of Hosen (Nitta District), followed by the village of Kesatoda (Yamada District) on December 1, 1963.