Dalarna County is a county or län in central Sweden (Svealand). It borders the counties of Uppsala, Jämtland, Gävleborg, Västmanland, Örebro, and Värmland. It also borders on the Norwegian counties of Hedmark and Trøndelag to the west. It was formerly known as Kopparberg County (Swedish: Kopparbergs län) until the name was changed to that of the provincial region on 1 January 1997. The province of Dalarna is slightly larger than the county, as the westernmost part of Ljusdal Municipality belongs to it.

The term Dalarna County is mainly used for administrative purposes; it is further divided into municipalities (kommuner). Dalarna County encompasses nearly all of the cultural and historical province of Dalarna (literally, "the valleys"). For the most part, sparsely populated and with extensive tracts of wilderness, Dalarna County is almost as large as Belgium in terms of land area.

In older times, Dalarna was periodically part of the territory ruled by the governor of Västerås Castle. The 1634 Instrument of Government led to the creation of a county covering Dalarna with its own County Governor. The Kopparbergs län (literally Copper Mountain County) was finally created by royal decree in 1647. In 1997, the name of the county was changed to Dalarna County.