Strömstad is a locality and the seat of Strömstad Municipality, Västra Götaland County, Sweden with 6,288 inhabitants in 2010. For historical reasons, Strömstad is called a city despite its small population. Strömstad became part of Sweden in 1658, as part of the Treaty of Roskilde, which transferred the Bohuslän province from Norway to Sweden. It achieved town status in 1676. Strömstad became an important sea-bathing and spa destination in the mid-19th century.