As of February 2014, the district has an estimated population of 38,078 and an area of 1404.55 km². The entire city of Takizawa, and most of the cities of Hachimantai and Morioka were formerly part of Iwate District.
The ancient county of Iwadenomori(岩出の森郡,Iwadenomori-gun?) in Mutsu Province dates from the early Heian period. Under the Tokugawa shogunate, Iwate county consisted of one town (Morioka) and 85 villages under the control of Morioka Domain. Following the Meiji restoration, Iwate District came under Rikuchū Province and became part of Iwate Prefecture in 1872. In January 1879, Iwate District was divided into Kita-Iwate District with 47 villages, and Minimi-Iwate District with 38 villages.
April 1, 1897 – With the establishment of the municipality system, Kita-Iwate District and Minami-Iwate District were merged to become Iwate District, and was organized into one town (Morioka and 24 villages)
December 23, 1940 - The village of Shizukuishi was elevated to town status. (2 towns, 21 villages)
April 10, 1941 - The villages of Asagishi, Nakano and Motomiya were merged into the city of Morioka. (2 towns, 18 villages)
July 1, 1948 - The town of Kuzumaki, and the village of Ekari were moved from Kunohe District to Iwate District. (3 towns, 19 villages)
April 1, 2002 - The town of Ashiro was moved from Ninohe District to Iwate District. (5 towns, 3 villages)
September 1, 2005 - The towns of Ashiro and Nishine, and the village of Matsuo were merged to create the city of Hachimantai. (3 towns, 2 villages)
January 10, 2006 - The village of Tamayama was merged into the expanded city of Morioka. (3 towns, 1 village)
January 1, 2014 - The village of Takizawa was elevated to city status. (3 towns)