Iwadeyama (岩出山町 Iwadeyama-machi) was a town located in Tamatsukuri District, Miyagi, Japan.
In 2003, the town had an estimated population of 13,476 and a population density of 95.78 persons per km². The total area was 140.70 km2 (54 sq mi).
On March 31, 2006, Iwadeyama was merged with the town of Naruko, from Tamatsukuri District, the towns of Kashimadai, Matsuyama and Sanbongi, all from Shida District, the town of Tajiri, from Tōda District, and the city of Furukawa to create the new city of Ōsaki. Tamatsukuri District and Shida District were dissolved as a result of this merger.