Mitsuishi (三石町 -chō) was a town that was located in Mitsuishi District, Hidaka, Hokkaidō, Japan.
On March 31, 2006 Mitsuishi was merged with the town of Shizunai, from Shizunai District, to form the new town of Shinhidaka, in the newly-created Hidaka District.
As of 2004, the town had an estimated population of 4,950 and a density of 14.30 persons per km². The total area was 346.23 km².