| Code | Name | Region |
|---|---|---|
| USOXH | Oxon Hill | MD |
| USOYB | Oyster Bay | NY |
| USYRC | Oyster Creek | TX |
| USOZR | Ozark | AL |
| USOZK | Ozark | AR |
| USORK | Ozark | MO |
| USOZA | Ozona | TX |
| USZ6O | Ozone | AR |
| USOZO | Ozone Park/queens/new York | NY |
| USZPO | Pablo | MT |
| USPBT | Pabst | GA |
| USOWJ | Owensville | IN |
| USOWV | Owensville | MO |
| USQOW | Owenton | KY |
| USOW7 | Owings | MD |
| USOWI | Owings Mills | MD |
| USO2W | Owingsville | KY |
| US2OH | Owls Head | ME |
| USOWO | Owosso | MI |
| USOXO | Oxford | AL |
| 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 |