Jämtland County (Swedish: Jämtlands län, Southern Sami: Jiemthen leene) is a county or län in the middle of Sweden consisting of the provinces of Jämtland and Härjedalen, along with minor parts of Hälsingland and Ångermanland, plus two small uninhabited strips of Lapland and Dalarna. Jämtland County constitutes 12 percent of Sweden's total area, 49,443 km2 (19,090 sq mi) and is the third largest county in the country. The county capital is Östersund and the county governor, appointed by the Swedish government, is Jöran Hägglund, who leads the administrative board. Jämtland County borders the counties of Dalarna, Gävleborg, Västernorrland, and Västerbotten. It also shares a border with the Norwegian county of Trøndelag.

The county was established in 1810 and its foundation has both domestic and foreign causes. Upon formation it only consisted of the provinces of Jämtland and Härjedalen, which is why the coat of arms is a shield parted per fess with their provincial arms.

Being sparsely populated, the land area of Jämtland County is larger than those of the Netherlands and Switzerland.