| Lagny-le-Sec | |
| Commune Status: | Commune |
| Arrondissement: | Senlis |
| Canton: | Nanteuil-le-Haudouin |
| Insee: | 60341 |
| Postal Code: | 60330 |
| Mayor: | Didier Doucet[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Pays de Valois |
| Coordinates: | 49.0875°N 2.745°W |
| Elevation M: | 107 |
| Elevation Min M: | 94 |
| Elevation Max M: | 116 |
| Area Km2: | 11.23 |
Lagny-le-Sec (in French pronounced as /laɲi lə sɛk/) is a commune in the Oise department in northern France.