Approximately 20 percent of the total population are foreign citizens, mostly Japanese Brazilians, who work at many factories in the town.

It is estimated that 15 percent of the population speak Portuguese as their native language,[2] and as of 2007, Ōizumi has the highest concentration of Brazilians of any city in Japan.

The villages of Ōkawa and Koizumi were created within Ōra District, Gunma Prefecture on April 1, 1889 with the creation of the modern municipalities system after the Meiji Restoration.

Ōizumi has a mayor-council form of government with a directly elected mayor and a unicameral town council of 14 members.

In terms of national politics, the town is part of Gunma 3rd district of the lower house of the Diet of Japan.