Complex sentence: The town was merged with Sanwa also from the Sashima District and the former city of Koga to form the new city of Koga and their town hall is used as the new Koga City Hall.
Split into simpler sentences: The town was merged with Sanwa also from Sashima District and the former city of Koga to form the new city of Koga. Sōwa's town hall is used as the new Koga City Hall.