Sweden is a nation-state on the Scandinavian peninsula of Earth's European continent. Stockholm is the capital city. A person or thing originating from Sweden is called Swedish.
Richard Daystrom was born in Göteborg, Sweden, in 2219. (Orion Press: "Lexicon, C-D", 2010 revision)
At least in the 2260s, the Federation Bureau of Penology's headquarters was in Stockholm. (TOS: "Dagger of the Mind")
Åse Sorensen, her husband Kristian Sorensen and their children Synni and Bror were born in Sweden. (Star Trek: The Cantabrian Expeditions: "Two Hit, One Stone")
Davin Andersen's parents were Swedish missionaries of the Foundationist movement. (Star Trek: Pendragon)
Cryptologic Technician, Second Class Martin Karlsson appeared to be Swedish. (Bait and Switch: "Shortest War Ever")