During the Edo period, the area of present-day Shimonita was largely part of the tenryō territory held directly by Tokugawa shogunate within Kōzuke Province.

The town of Shimonita was created within Kitakanra District of Gunma Prefecture on April 1, 1889 with the creation of the modern municipalities system after the Meiji Restoration.

Shimonita has a mayor-council form of government with a directly elected mayor and a unicameral town council of 12 members.

Shimonita, together with the other municipalities in Kanra District contributes one member to the Gunma Prefectural Assembly.

In terms of national politics, the town is part of Gunma 5th district of the lower house of the Diet of Japan.