Söderköping Municipality is a municipality in Östergötland County in southeast Sweden. Its seat is located in the city of Söderköping.

Östergötland County is a county or län in southeastern Sweden. It has land borders with the counties of Kalmar to the southeast, Jönköping to the southwest, Örebro to the northwest, and Södermanland to the northeast. It also has a sea border with Västra Götaland to the west, and borders the Baltic Sea to the east.