| Conventional Long Name: | Viborg and Nyslott County1 |
| Native Name: | Viborgs och Nyslotts län Viipurin ja Savonlinnan lääni |
| Common Name: | Viborg and Nyslott |
| Subdivision: | County |
| Nation: | the Swedish Empire |
| Year Start: | 1634 |
| Event Start: | Established |
| Event End: | Treaty of Nystad |
| Year End: | 1721 |
| Date End: | 30 August |
| Event1: | Great Northern War |
| Date Event1: | 1700–21 |
| S1: | County of Kymmenegård and Nyslott |
| Flag S1: | Flag of Sweden.svg |
| S2: | Saint Petersburg Governorate |
| Flag S2: | Flag of Russia.svg |
| Capital: | Vyborg |
| Footnotes: | 1 Prior to 1658 it was known as the County of Karelia (Swedish: Karelens län, Finnish: Karjalan lääni). |
Viborg and Nyslott County (Swedish: Viborgs och Nyslotts län, Finnish: Viipurin ja Savonlinnan lääni) was a county of the Swedish Empire from 1634 to 1721. The county was named after the castle towns of Viborg (Finnish: Viipuri) and Nyslott (Finnish: Savonlinna, literally New Castle), today located in the towns of Vyborg in Russia and Savonlinna in Finland.
The county was established in 1634 as Karelia County (Swedish: Karelens län, Finnish: Karjalan lääni), but in 1641 Nyslott County (Swedish: Nyslotts län, Finnish: Savonlinnan lääni) was broken out and made a separate entity. Remainder of Karelia County was now called Viborg County. In 1650 the counties were joined again as the Viborg and Nyslott County.
Following the Great Northern War southeastern parts of the county were ceded to Russia in 1721, and the territory that remained was reconstituted into the County of Kymmenegård and Nyslott (Swedish: Kymmenegårds och Nyslotts län, Finnish: Savonlinnan ja Kymenkartanon lääni), with the northern and western parts of County of Kexholm. In 1743 following a new conflict part of this county was also ceded to Russia in the Treaty of Åbo. The ceded parts of the County of Viborg and Nyslott and the County of Kexholm were at first part of the Saint Petersburg Governorate, but in 1744 they were reconstituted with new conquests into the Russian Vyborg Governorate, which also became known as Old Finland. Remainder of the County of Kymmenegård and Nyslott was joined with some parts of the County of Nyland and Tavastehus in 1747 into the County of Savolax and Kymmenegård.
After the Russian victory in the Finnish War in 1809, Sweden ceded all its territory in Finland to Russia by the Treaty of Fredrikshamn. As part of Russian Empire Finland became to constitute a separate grand duchy. In 1812 Russia made the territories of Vyborg Governorate part of the new Grand Duchy of Finland as Viipuri Province.