Izumo Province (出雲国, Izumo-no-kuni) was an old province of Japan which today consists of the eastern part of Shimane Prefecture. It was sometimes called Unshū (雲州). The province is in the Chūgoku Region.
During the early Kofun period (3rd century) this region was independent and constructed rectangular tumuli. But in the fourth century this region saw the construction of rectangular and key shaped tumuli.
During the 6th or 7th century it was absorbed due to the expansion of the state of Yamato, within which it assumed the role of a sacerdotal domain.
Even today, the Izumo Shrine constitutes (as does the Grand Shrine of Ise) one of the most important sacred places of Shinto: it is dedicated to kami, especially to Ōkuninushi (Ō-kuni-nushi-no-mikoto), mythical progeny of Susanoo and all the clans of Izumo. The mythological mother of Japan, the goddess Izanami, is said to be buried on Mt. Hiba, at the border of the old provinces of Izumo and Hōki, near modern-day Yasugi of Shimane Prefecture.
By the Sengoku period, Izumo had lost much of its importance. It was dominated before the Battle of Sekigahara by the Mōri clan, and after Sekigahara, it was an independent fief with a castle town at modern Matsue.
In Japanese mythology, the entrance to Yomi (Hell, land of the dead) was located within the province, and was sealed by the god Izanagi by placing a large boulder over the entrance.