| Hope Observatory | Maryland | — |
| Hornsby Bend Bird Observatory | Texas | — |
| Houston observatory | Houston | — |
| Howell Observatory | Misisipi | — |
| Hudson observatory | Nuevo Hampshire | — |
| Hume Observatory | Mark West Springs | — |
| HUT observatory | Edwards | — |
| Hyde Memorial Observatory | Nebraska | — |
| Ibis observatory | Manhattan | — |
 Imaging X-ray Polarimetry Explorer | — | — |
| Indian Hill North Observatory | Huntsburg | — |
| Insperity observatory | Humble | — |
| Instituto de Investigaciones Astronómicas de Pisgah | Carolina del Norte | — |
| Iowa Robotic Observatory | Elgin | — |
| Ironwood observatory | Haleiwa | — |
| Ironwood Remote observatory | Honolulu County | — |
| Irvine–Michigan–Brookhaven | — | — |
| ISON-NM Observatory | Mayhill | 2.217 m |
| ITelescope SRO Observatory | Alder Springs | — |
| Ivywood observatory | Edmond | — |
| J. C. Veen observatory | Municipio de Lowell | — |
| Jack C. Davis Observatory | Carson City | — |
| Jack C. Davis Observatory | Nevada | — |
| Jarnac Observatory | Vail | — |
 Jennifer Chalsty Planetarium | Jersey City | — |
 Jewett Observatory | Pullman | 790 m |
| Jim Carrigan Magnetic Observatory | — | — |
| Jimginny Observatory | Naperville | — |
| John H. Witte, Jr. Observatory | Iowa | — |
| John J. McCarthy Observatory | New Milford | — |
 John Payson Williston Observatory | — | — |
| Joint observatory for cometary research | Socorro | — |
 Jones Observatory | Chattanooga | — |
| Jornada Observatory | Las Cruces | — |
| JPL SynTrack Robotic Telescope | Alder Springs | — |
| JPL SynTrack Robotic Telescope 2 | Alder Springs | — |
| JPL SynTrack Robotic Telescope 3 | Flagstaff | — |
| Judson B. Coit Observatory | — | — |
| Kachina observatory | Kachina Village | — |
| Kalamazoo observatory | Municipio de Kalamazoo | — |
| Kanab observatory | Cannabis sativa | — |
| Katy Observatory | Texas | — |
| Kaua‘i Educational Association for Science and Astronomy | — | — |
 Keeble Observatory | Virginia | — |
 Kennon Observatory | Misisipi | — |
| Kenwood Astrophysical Observatory | Illinois | — |
| Killer Rocks Observatory | Pie Town | — |
| Kingsnake Observatory | Seguin | 140 m |