| Thiernu | |
| Commune Status: | Commune |
| Arrondissement: | Laon |
| Canton: | Marle |
| Insee: | 02742 |
| Postal Code: | 02250 |
| Mayor: | Jean-Claude Guérin[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Pays de la Serre |
| Coordinates: | 49.7617°N 3.7897°W |
| Elevation M: | 89 |
| Elevation Min M: | 78 |
| Elevation Max M: | 157 |
| Area Km2: | 6.16 |
Thiernu (pronounced as /fr/) is a commune in the Aisne department in Hauts-de-France in northern France.