Sepienko was formerly part of the German Empire. In the German Empire, the place was called Hardtbruch.
The place is now called Sepienko and belongs to Poland.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Sepienko | German Empire | Kosten | before the Versailles Treaty |
| Sepienko | Poland | Kościan | after the Versailles Treaty |
| Hardtbruch | German Empire | Kosten (Wartheland) | 1939 |
| Sepienko | Poland | Kościan | 1945 |
| Sepienko | Poland | Leszno | 1992 |