Os within Hedmark
|Administrative centre||Os i Østerdalen|
|• Mayor (2011)||Arnfinn Nergård (Sp)|
|• Total||1,040 km2 (400 sq mi)|
|• Land||1,008 km2 (389 sq mi)|
|Area rank||101 in Norway|
|• Rank||333 in Norway|
|• Density||2/km2 (5/sq mi)|
|• Change (10 years)||4.2 %|
|Time zone||CET (UTC+1)|
|• Summer (DST)||CEST (UTC+2)|
|ISO 3166 code||NO-0441|
|Official language form||Neutral|
Os is a municipality in Hedmark county, Norway. It is part of the traditional region of Østerdalen. The administrative centre of the municipality is the village of Os i Østerdalen. The new municipality of Os was separated from Tolga on 1 July 1926. (Tolga and Os were also briefly merged from 1966-1976: see Tolga-Os.)
The municipality is located to the west of the municipality of Røros and to the south of Midtre Gauldal and Holtålen in Sør-Trøndelag county. In Hedmark county, Os is east of Tolga and north of Engerdal.
The municipality (originally the parish) is named after the old Os farm (Old Norse: Óss), since the first church was built here (in 1703). The name is identical with the word óss which means "mouth of a river" (here it is the Vangrøfta river running out into the Glomma river).
The coat-of-arms is from modern times. They were granted on 17 December 1992. The arms show three gold cowbells on a green background. It symbolizes the traditional and modern businesses in the municipality.
Lakes in the region include Flensjøen.