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 (, ), 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.