Olszewo was formerly part of the German Empire. In the German Empire, the place was called Elsenhof.
The place is now called Olszewo and belongs to Poland.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Olszewo | Russian Empire | Serpec | 1914 |
| Olszewo | Poland | Sierpc | 1919 |
| Elsenhof | German Empire | Sichelberg | 1939 |
| Olszewo | Poland | Żuromin | 1945 |
| Olszewo | Poland | Ciechanów | 1992 |