Sielec was formerly part of the German Empire. In the German Empire, the place was called Sielec.
The place is now called Sielec and belongs to Poland.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Sielec | Russian Empire | Plonsk | 1914 |
| Sielec | Poland | Płońsk | 1919 |
| Sielec | German Empire | Plöhnen | 1939 |
| Sielec | Poland | Płońsk | 1945 |
| Sielec | Poland | Płock | 1992 |