Ślesin [ˈɕlɛɕin] is a town in Konin County, Greater Poland Voivodeship, Poland, with 3,324 inhabitants (2004). In partitioned Poland it belonged to the Russian-controlled Congress Kingdom from 1815; it returned to Poland when the country regained its independence in 1918. During World War II, Ślesin was occupied by the Wehrmacht on 13 September 1939, annexed to Nazi Germany from 1939 to 1945 and administered as part of Reichsgau Wartheland.