| OGD | KOGD | Ogden Municipal Airport | Ogden | |
| - | - | Ohio Co | Hartford | |
| HLG | KHLG | Ohio County Airport | Wheeling | |
| - | - | Ohio Dusting Co Inc | Pandora | |
| ATO | KUNI | Ohio University Airport | Athens | |
| - | - | Ojibwa | Weidman | |
| - | - | Okanogan Legion | Okanogan | |
| OBE | KOBE | Okeechobee County Airport | Okeechobee | |
| - | - | Okeene Municipal | Okeene | |
| - | - | Okemah | Okemah | |
| DWN | - | Oklahoma City Downtown Airpark | Oklahoma City | |
| OKM | KOKM | Okmulgee Airport | Okmulgee | |
| - | - | Okolona Mun-Stovall | Okolona | |
| - | - | Oktibbeha | Starkville | |
| - | - | Olcott-Newfane | Olcott | |
| - | - | Old Bridge | Old Bridge | |
| - | - | Old Hoppe Place | Agua Dulce | |
| - | - | Old Mans | Pedrictown | |
| OLD | KOLD | Old Town Airport | Old Town | |
| - | - | Oldham Co | Vega | |
| NEN | - | Olf Usn Airport | Whitehouse | |
| - | POLI | Oliktok Lrrs | Oliktok Point | |
| - | - | Olive Hill-Seller'S | Olive Hill | |
| - | KOVL | Olivia Regional | Olivia | |
| - | - | Olla | Olla | |
| OLY | KOLY | Olney Airport | Olney | |
| ONY | KONY | Olney Airport | Olney | |
| - | - | Olustee Municipal | Olustee | |
| - | - | Ona | Milton | |
| OEA | KOEA | Oneal Airport | Vincennes | |
| UCA | KUCA | Oneida County Airport | Utica | |
| ONH | - | Oneonta Municipal Airport | Oneonta | |
| - | - | Onida Municipal | Onida | |
| ONN | - | Onion Bay Airport | Onion Bay | |
| - | KOGM | Ontonagon Co | Ontonagon | |
| - | - | Opa Locka West Airport | Miami | |
| - | - | Opheim | Opheim | |
| - | KORC | Orange City Municipal | Orange City | |
| - | KOMH | Orange Co | Orange | |
| - | KORG | Orange Co | Orange | |
| MGJ | KMGJ | Orange County Airport | Montgomery | |
| - | KNOG | Orange Grove Nalf | Orange Grove | |
| - | KORE | Orange Municipal | Orange | |
| OGB | KOGB | Orangeburg Municipal Airport | Orangeburg | |
| - | - | Orlando Country | Plymouth | |
| - | - | Orleans | Orleans | |
| - | KOMN | Ormond Beach Municipal | Ormond Beach | |
| - | - | Orofino Municipal | Orofino | |
| - | - | Orogrande | Orogrande | |
| OVE | KOVE | Oroville Airport | Oroville | |