Sielec Nowy was formerly part of the German Empire. In the German Empire, the place was called Neusiedel.
The place is now called Sielec Nowy and belongs to Poland.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Neu-Sielec | German Empire | Rawitsch | before the Versailles Treaty |
| Sielec Nowy | Poland | Rawicz | after the Versailles Treaty |
| Neusiedel | German Empire | Rawitsch | 1939 |
| Sielec Nowy | Poland | Rawicz | 1945 |
| Sielec Nowy | Poland | Leszno | 1992 |