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, Plassen, and Tørberget.

The 3,014-square-kilometre (1,164 sq mi) municipality is the 15th largest by area out of the 357 municipalities in Norway. Trysil Municipality is the 152nd most populous municipality in Norway with a population of 6,542. The municipality's population density is 2.2 inhabitants per square kilometre (5.7/sq mi) and its population has decreased by 0.8% 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 in the western part of Trysil Municipality (population: 302) was transferred to the neighboring Åmot Municipality. 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 Municipality.

Historically, the municipality was part of Hedmark county. On 1 January 2020, the municipality became a part of the newly-formed Innlandet county (after Hedmark and Oppland counties were merged).

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" (Norwegian: 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. The arms were designed by Bjørn Ellefsæter. The municipal flag has the same design as the coat of arms.

The Church of Norway has seven parishes (sokn) within Trysil Municipality. It is part of the Sør-Østerdal prosti (deanery) in the Diocese of Hamar.

One of the first-known, organized ski races was held here 22 January 1862. Roland Huntford, author of Two Planks and a Passion, describes this race as, "the first truly modern ski race." The famous Norwegian skier Halvard Morgedal won all the competitions that year. The Trysilgutten ski club, founded in 1861, is one of the world's oldest ski clubs. See also the Kiandra snow shoe club and Onion Valley snow shoe club.