The Irish state has officially approved the following list of national monuments in County Longford. In the Republic of Ireland, a structure or site may be deemed to be a "national monument", and therefore worthy of state protection, if it is of national importance. If the land adjoining the monument is essential to protect it, this land may also be protected.
National Monuments
edit| NM# | Monument name | Description | Image | Townland | Location |
|---|---|---|---|---|---|
| 630 | Aghaward fort | Ringfort | Aghaward | 53°47′32″N 7°38′41″W / 53.792357°N 7.644732°W | |
| 677 | Corlea Trackway | Timber Trackway |  | Corlea | 53°37′25″N 7°52′22″W / 53.623543°N 7.87267°W |
| 91 | Inchcleraun | Early Medieval Ecclesiastical Site | Inchcleraun | 53°35′06″N 8°00′40″W / 53.584863°N 8.011179°W | |
| 640 | Larkfield fort | Ringfort | Larkfield | 53°50′30″N 7°32′46″W / 53.841538°N 7.546034°W | |
| 263 | Granard Motte | Motte & Bailey |  | Granard | 53°46′35″N 7°30′07″W / 53.776312°N 7.501945°W |
| 598 | Sonnagh fort | Ringfort | Sonnagh | 53°49′51″N 7°36′02″W / 53.830744°N 7.600570°W |