| Code | Name | Region |
|---|---|---|
| USOXC | Oxford | CT |
| USOFD | Oxford | FL |
| USOXG | Oxford | GA |
| USOXA | Oxford | IA |
| USOFC | Oxford | IN |
| USOXB | Oxford | MA |
| USOXU | Oxford | MD |
| USOX2 | Oxford | ME |
| USOFM | Oxford | MI |
| USUOX | Oxford | MS |
| USOXF | Oxford | NC |
| USVEK | Overbrook | KS |
| US3QW | Overgaard | AZ |
| USOVD | Overland | MO |
| USOVL | Overland Park | KS |
| USOVR | Overpeck | OH |
| USOV9 | Overton | NE |
| USOV4 | Overton | TX |
| USGHJ | Overton, Clark | NV |
| USOD2 | Ovid | ID |
| USZG4 | Ovid | MI |
| USVID | Ovid | NY |
| USZOD | Oviedo | FL |
| USOVP | Ovilla | TX |
| USOW3 | Owasso | OK |
| USOWA | Owatonna | MN |
| USOWG | Owego | NY |
| USZOE | Owen | WI |
| USODL | Owendale | MI |
| USOQS | Owens Cross Roads | AL |
| USOWB | Owensboro | KY |
| USTGH | Otsego | MI |
| USUY7 | Otsego | MN |
| USOTW | Ottawa | IL |
| USOTR | Ottawa | KS |
| USW8T | Ottawa | MN |
| USOTQ | Ottawa | OH |
| USOTL | Ottawa Lake | MI |
| USIXO | Otter River | MA |
| USO2T | Otterbein | IN |
| USOIM | Otterville | MO |
| USI8C | Otto | NC |
| USOTO | Otto | NM |
| USTOV | Ottoville | OH |
| USOSV | Ottsville | PA |
| USOTM | Ottumwa | IA |
| USOVZ | Otwell | AR |
| USOUR | Ouray | CO |
| US3VC | Outlook | WA |
| USKOZ | Ouzinkie | AK |