Viborg and Nyslott County, Viborgs och Nyslotts län or Viipurin ja Savonlinnan lääni, was a county of Sweden from 1634 to 1721, when by the Treaty of Nystad Vyborg was ceded to Russia. The remaining areas were renamed Kymmenegårds and Nyslott County. These were also ceded to Russia in 1743. In 1812 the conquered lands were added to the Grand Duchy of Finland as Viborg County (Viborgs län/Viipurin lääni).

After the Treaty of Nöteborg (1323), particularly during the Kalmar Union (1397–1521), the governors of Viborg had a relatively independent relationship to the state authorities in Stockholm and Copenhagen. Their district, Viborgs län, virtually functioning like contemporary German margravates.

After World War II the Soviet Union annexed parts of the area and the remainder was renamed Kymi Province. In the reform in 1997 it was added to the Province of Southern Finland.

See also

• län
• Finnish Karelia
• Old Finland