| Carbuncle Hill Observatory | Coventry | — |
| Carla Jane Observatory | Charlotte | — |
| Carroll observatory | Condado de Santa Bárbara | — |
| Cascade Mountain observatory | Cascade Mountain | — |
| Catalina 40" Telescope | Pima County | 2.791 m |
| Catholic University Observatory | Washington D. C. | — |
| CBA Concord observatory | Tucson | — |
| CBA-East Observatory, Laurel | North Laurel | — |
| CBA-MM Observatory | Bass Lake | — |
| CBA-NOVAC Observatory, | Front Royal | — |
| Cedar Drive Observatory | Hofa Park | — |
| Cedar Glen Observatory | Lake Arrowhead | — |
| Cedar Knolls observatory | Municipio de Hanover | — |
| Celestial Observatory | Arkansas | — |
| Centennial Observatory | Twin Falls | — |
| Cewanee Observatory at DSNM | New Mexico | — |
 Chabot Space and Science Center | Oakland | — |
| Chapel Hill observatory | Texas | — |
| Cherokeeridge Observatory | Fort Madison | — |
 Chico Community Observatory | California | — |
| Chinle observatory | condado de Apache | — |
| Chula Observatory | Chula | — |
| Clarke Observatory | Ohio | — |
 Class of 1951 Observatory | — | — |
| Clay Center Observatory, Brookline | Brookline | — |
| Clay Telescope observatory | Cambridge | — |
| Clinton observatory | Maryland | — |
 Cloudcroft Observatory | New Mexico | 2.751 m |
| College Magnetic Observatory | — | — |
 Collins Observatory | Nueva York | — |
| Comet Hunter Observatory 2 | Pensilvania | — |
| Command Module Observatory | Tempe | — |
| Conlin Hill Observatory | Oxford | — |
| Conway observatory | Conway | — |
| Cordell–Lorenz Observatory | Tennessee | — |
 Coriolis | — | — |
| Corpus Christi observatory | Corpus Christi | — |
| Corralitos Observatory | New Mexico | — |
| Cosmos Research Center | California | — |
| Cottonwood Observatory | Oklahoma | — |
| Crane Observatory | Kansas | — |
| Crawfordville Observatory | Sharon | — |
| Creighton University Observatory | Nebraska | — |
| Crescent Moon Observatory | Cristóbal Colón | — |
 Crow Observatory | Misuri | — |
| CS3-DanHenge Observatory | Landers | — |
| CS3-Palmer Divide Station | Landers | — |
| CS3-Trojan Station | Landers | — |