Moernach was formerly part of the German Empire. In the German Empire, the place was called Mörnach.
The place is now called Mœrnach and belongs to France.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Mörnach | German Empire | Altkirch | before the Versailles Treaty |
| Moernach | France | Haut-Rhin | after the Versailles Treaty |
| Mörnach | German Empire | Altkirch | 1940 |
| Mœrnach | France | Haut-Rhin | 1945 |
| Mœrnach | France | Haut-Rhin | 1993 |