Trysil is a municipality in Innlandet county, Norway. It is located in the traditional district of Østerdalen. The administrative centre of the municipality is the village of Innbygda. Other villages in the municipality include Nybergsund, Østby, and Tørberget.
The municipality is the 15th largest by area out of the 356 municipalities in Norway. Trysil is the 150th most populous municipality in Norway with a population of 6,603. The municipality's population density is and its population has decreased by 2.2% over the previous 10-year period.
On 1 January 1838, the prestegjeld of Trysil was established as a civil municipality (see formannskapsdistrikt law). In 1880, the Osneset area of western Trysil (population: 302) was transferred to the neighboring municipality of Åmot. On 1 January 1911, the northern part of the municipality (population: 291) was separated to join the new Engerdal Municipality. There were also some minor boundary adjustments west of the lake Osensjøen in 1943 and again in 1964 when some areas were transferred from Elverum Municipality to Trysil.
The municipality (originally the parish) is named after the old Trysil farm which was most likely the original name of the current Prestgarden ("the vicarage"), where the first Trysil Church was built. The first element possibly comes from the name of a local river, Trya. The meaning of the river name is unknown. The last element is sil which means "quiet stretch of a river". Prior to 1906, the name was spelled "Tryssil".
The coat of arms was granted on 21 October 1991. The official blazon is "Azure, two ski poles issuant from the base pointing up" (I blått to oppvoksende sølv skistaver). This means the arms have a blue field (background) and the charge is two vertical ski poles pointing upwards. The charge has a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. The design is meant to symbolize Trysil in the past, present, and future since skiing has long been an important way of transportation over the years (including the legend of Trysil-Knut), but has more recently become a major tourist attraction.