| Saint-Hernin | |
| Native Name: | Sant-Hern |
| Commune Status: | Commune |
| Coordinates: | 48.2183°N -3.6331°W |
| Elevation Min M: | 59 |
| Elevation Max M: | 308 |
| Insee: | 29250 |
| Postal Code: | 29270 |
| Arrondissement: | Châteaulin |
| Canton: | Carhaix-Plouguer |
| Mayor: | Marie-Christine Jaouen[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Poher |
| Area Km2: | 29.29 |
Saint-Hernin (in French pronounced as /sɛ̃.t‿ɛʁnɛ̃/; Breton: Sant-Hern) is a commune in the Finistère department of Brittany in north-western France. The historian and librarian Georges Le Rider (1928-2014) was born in Saint-Hernin.
Inhabitants of Saint-Hernin are called in French Saint-Herninois.
Saint-Hernin lies on the northern slope of the Montagnes Noires (french, Black Mountains). The canal de Nantes à Brest, which is the canalized river Hyères, forms the commune's northern border.