On November 1, 2004 - the old city of Saijō absorbed the city of Tōyo, and the towns of Komatsu and Tanbara (both from Shūsō District) to create the new and expanded city of Saijō. Shūsō District was dissolved as a result of this merger.
On January 1, 2005 - the village of Hirota (from Iyo District) was merged into the expanded town of Tobe.