| Mennessis | |
| Commune Status: | Commune |
| Arrondissement: | Laon |
| Canton: | Tergnier |
| Insee: | 02474 |
| Postal Code: | 02700 |
| Mayor: | Antoine De Abreu[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | CA Chauny Tergnier La Fère |
| Coordinates: | 49.6947°N 3.2736°W |
| Elevation M: | 70 |
| Elevation Min M: | 54 |
| Elevation Max M: | 88 |
| Area Km2: | 5.23 |
Mennessis is a commune in the Aisne department in Hauts-de-France in northern France. Mennessis station has rail connections to Saint-Quentin, Amiens, Compiègne and Laon.