Sønderby-Østerby was formerly part of the German Empire. In the German Empire, the place was called Sönderby-Osterby.
The place is now called NN and belongs to Denmark.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Sönderby-Osterby | German Empire | Sonderburg | before the Versailles Treaty |
| Sønderby-Østerby | Denmark | Sønderborg | after the Versailles Treaty |
| NN | Denmark | Sønderjylland | 1993 |