The Vikings mostly came from various places in Scandinavia. The kingdom of Sweden was not technically founded until around the 1100, but many people's of southern Sweden participated in coastal raiding and would be considered what we call "Vikings" now. In fact There were several years very prosperous swedish settlements that grew during the Viking age, like Visby and many others near the øresund and Kattegat straits. Many warriors from what is now Sweden travelled all over Europe and beyond working as mercenaries, as Vikings often did. Famously, the varangian guard, the personal retinue of several Byzantine emperor's, would have included many of these man. I hope this answers your question!