On October 1, 2005 the towns of Ogawa and Bato from Nasu District merged to form the new town of Nakagawa.
On January 10, 2006, the town of Minamikawachi from Kawachi District, the town of Ishibashi and the village of Kokubunji (both from Shimotsuga District) merged to form the new city of Shimotsuke.
On March 20, 2006, the city of Imaichi, the town of Ashio from Kamitsuga District, the town of Fujihara and the village of Kuriyama (both from Shioya District) merged with the old city of Nikko to form the new city of Nikko.