Sonfjället National Park, National park in Härjedalen, Sweden.

Sonfjället National Park protects an isolated mountain massif south of the Ljusnan near Hede, with Högfjället rising to 1,277 meters. Below the bare peaks lie wooded slopes and partly untouched birch forests and wetlands. The park covers 104 square kilometers after the 1989 expansion.

The park was established in 1909 as one of Europe's early protected areas, with a major expansion in 1989. These two milestones shaped how the landscape has been conserved over time.

The name Sonfjället has two spellings: authorities used Sånfjället from 1919 to 2010 to match pronunciation, but Härjedalen residents preferred o, and the official form reverted to Sonfjället in 2010. The first element may derive from Old West Norse sunna, 'sun', though modern place-name scholars reject this because it conflicts with the local dialect pronunciation.

The park is open year-round, with summer and early autumn offering the best hiking conditions. Visitors should prepare for variable weather and wear sturdy footwear, as trails can become muddy or slippery depending on recent rainfall.

The brown bear is sometimes called Sonfjället's signature species, and the area is among Sweden's densest for bears. The park was also created in 1909 partly to protect Sweden's last remnant of wild reindeer, and its lichen-rich heaths were chosen because reindeer grazing had barely touched them.