Söderköping is a locality and the seat of Söderköping Municipality, Östergötland County, Sweden with 6,992 inhabitants in 2010. Söderköping is, despite its small population, for historical reasons normally still referred to as a town. Statistics Sweden, however, only counts localities with more than 10,000 inhabitants as cities. Söderköping is about 15 km southeast of the city of Norrköping.