On November 1, 2004 - the town of Jūō (from Taga District) was merged into the expanded city of Hitachi. Taga District was dissolved as a result this merger.
On September 12, 2005 - the old city of Koga absorbed the towns of Sanwa and Sōwa (both from Sashima District) to create the new and expanded city of Koga.
On October 1, 2005 - the old city of Ishioka absorbed the town of Yasato (from Niihari District) to create the new and expanded city of Ishioka.
On October 11, 2005 - the town of Hokota absorbed the villages of Asahi and Taiyō (all from Kashima District) to create the city of Hokota. Kashima District was dissolved as a result of this merger.
On January 1, 2006 - the town of Ishige (from Yūki District) was merged into the expanded city of Mitsukaido. Mitsukaido changed the name to Jōsō at the same time.