The island was formerly administered as part of Shimushiru District of Nemuro Subprefecture of Hokkaidō.

In spite of its temperate latitude, the powerful Oyashio Current on the western flank of the Aleutian Low gives Simushir a chilly and very wet subarctic climate (Köppen Dfc) that amazingly almost qualifies as a polar climate (ET), which in low-lying areas would be expected only at latitudes about 20 degrees or 2,200 kilometres (1,370 mi) further north.

However, the extreme winds, which in winter average as much as 43 kilometres per hour (27 mph), make it feel much colder.

Sunshine is actually most likely in the wettest months of September and October when the heavy rain removes the low-level fog, but clear days are extremely rare at any time of year.

Météo Climat (records) [8] In the spring crested and least auklet, Leach's storm petrel, and Japanese cormorant nest on the island.