Mergers
- On March 22, 2005, the town of Mitsu, from Mitsu District, and the town of Nadasaki, from Kojima District, merged into the city of Okayama.
- On January 22, 2007, the town of Takebe, from Mitsu District, and the town of Seto, from Akaiwa District, merged into the city of Okayama.
Kojima, Mitsu, and Akaiwa districts have all since been dissolved.