Jednorozec was formerly part of the German Empire. In the German Empire, the place was called Jednorozec.
The place is now called Jednorożec and belongs to Poland.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Jednorozec | Russian Empire | Prasnyš | 1914 |
| Jednorożec | Poland | Przasnysz | 1919 |
| Jednorozec | German Empire | Praschnitz | 1939 |
| Jednorożec | Poland | Przasnysz | 1945 |
| Jednorożec | Poland | Ostrołęka | 1992 |