シュレースヴィヒ公国
The Duchy of Schleswig-Holstein-Sonderburg-Plön (), also "Schleswig-Holstein-Plön", "Holstein-Plön" or just "Duchy of Plön", was a small sub-duchy ("Teilherzogtum") created by the physical division of the Duchy of Schleswig-Holstein-Sonderburg. Today, its remaining significance is primarily the building of Plön Castle. The Duchy of Plön was not a territorial dukedom in its own right, but a sub-division within the state structure of the duchies of Schleswig and Holstein. The scattered territorial dominion lay mostly in the southeast part of present-day German state of Schleswig-Holstein.