Snillfjord is a municipality in Sør-Trøndelag county, Norway. It is part of the Fosen region. The administrative centre of the municipality is the village of Krokstadøra. Other villages in Snillfjord include Ytre Snillfjord, Hemnskjela, and Vutudal.
The municipality of Snillfjord was established on 1 July 1924 when it was separated from Hemne. The initial population was 776. On 1 January 1964, the eastern part of Heim (population: 724) and the western part of Agdenes (population: 196) was merged with Snillfjord (population: 681) to form a new, larger municipality of Snillfjord. On 1 January 1995, the Midtun area of Agdenes (population: 21) was transferred to Snillfjord. A road to the area had recently built, but it connected to Snillfjord and not Agdenes, so it was decided to switch to the other municipality due to the newly opened road connection.
The municipality is named after the Snillfjorden. The first element is probably an old river name of the Snilldalselva. The river name is derived from snild which comes from the word snjallr which means "fast".The coat-of-arms is from modern times. They were adopted on 19 September 1990. The arms show a silver pitchfork pointing dowm on a green background. It symbolizes the importance of agriculture in the municipality.