Izumo Province was in the Sanindō, or Sanin Region, an area encompassing provinces in the western portion of Honshū along the Sea of Japan.
In current terms, Izumo corresponds to the eastern portion of Shimane Prefecture. The province was comprised of ten districts, including Ou, Nogi, Shimane, Aika, Tatenui, Izumo, Kando, Iishi, Nita, and Ōhara. The provincial capital was in the city of Matsue.
A majority of the legends regarding the origin of Japan are associated with Izumo or surrounding areas, having a major influence on spiritual matters.
In the Sengoku period, the Amago clan governed Izumo and the neighboring province of Hōki. The Kizuki no Ōyashiro was in the western portion of Izumo administered by the Izumo kokusō. The Kizuki-no-Ōyashiro is a shrine of great historical significance. Prior to the Sengoku period, the eastern portion of Izumo was governed by the shōen shugo with ironworks being the primary industry. The Amago governed from their base at Gassantoda Castle.
1441-1470: Kyōgoku Mochikiyo
1470-1471: Kyōgoku Magodōjimaru
1472-1473: Kyōgoku Takakiyo
1473-1508: Kyōgoku Masatsune
1508-15xx: Kyōgoku 吉童子丸
1551-1560: Amago Haruhisa
1560-1566: Amago Yoshihisa
1542: The First Battle of Gassantoda Castle – Amago Haruhisa (approx. 20,000 men) vs. Ōuchi Yoshitaka and Mōri Motonari (size of army unknown)
1562-1563: The Battle of Shiraga Castle – Mōri (approx. 20,000 men led by Mōri Motonari, Kikkawa Motoharu, Kobayakawa Takakage) vs. Amago (approx. 12,000 men led by Amago Tomohisa)
1565: The Second Battle of Gassantoda Castle – Mōri (approx. 35,000 men led by Mōri Motonari, Kikkawa Motoharu, Kobayakawa Takakage) vs. Amago (approx. 10,000 men led by Amago Yoshihisa, Amago Tomohisa, Amago Hidehisa)
1570: The Battle of Fubeyama – Mōri (approx. 13,000 men led by Mōri Terumoto, Kikkawa Motoharu, Kobayakawa Takakage) vs. former retainers of the Amago (approx. 6,800 men led by Amago Katsuhisa, Yamanaka Yukimori, Tachihara Hisatsuna)
Shrines with the highest ranking (ichi-no-miya):
- Kizuki-no-Ōyashiro (currently known as the Izumo-Ōyashiro) in the Izumo District – the shrine was administered by the Senge and Kitajima families serving as kokusō, or local officials in charge of religious services and affairs. The Senge and Kitajima came from an ancient lineage comparable in duration to the Imperial household.
- Kuma-no-taisha located in the city of Matsue