Uusikaupunki is a town and municipality of Finland. It is located in the Southwest Finland region, 71 kilometres (44 mi) northwest of Turku and 97 kilometres (60 mi) south of Pori. The municipality has a population of 14,938 and covers an area of 551.65 square kilometres (212.99 sq mi) of which 49.04 km2 (18.93 sq mi) is inland water. The population density is 29.68 inhabitants per square kilometre (76.9/sq mi).

The Treaty of Nystad was the last peace treaty of the Great Northern War of 1700–1721. It was concluded between the Tsardom of Russia and the Swedish Empire on 10 September [O.S. 30 August] 1721 in the then Swedish town of Nystad. Sweden had settled with the other parties in Stockholm and in Frederiksborg (1720).