| Code | Name | Region |
|---|---|---|
| USOIN | O'brien | FL |
| USOCF | Ocala | FL |
| USO9C | Occidental | CA |
| USOCY | Ocean | NJ |
| USOB3 | Ocean Beach | CA |
| USOCE | Ocean City | MD |
| USOEC | Ocean City | NJ |
| USOAM | Ocean Gate | NJ |
| USOBH | Ocean Isle Beach | NC |
| USOCA | Ocean Reef | FL |
| USOS8 | Ocean Shores | WA |
| USIM5 | Oaklandon | IN |
| USOQY | Oakley | CA |
| USKLY | Oakley | IL |
| USOQK | Oakley | KS |
| USOK4 | Oakley | MI |
| USOK8 | Oakley | UT |
| USOXM | Oakman | AL |
| USUXS | Oakmont | PA |
| USOQR | Oakridge | OR |
| USOAS | Oaks | PA |
| USOKU | Oakton | VA |
| USOTN | Oaktown | IN |
| USOVY | Oakville | CA |
| USOKV | Oakville | CT |
| USV6L | Oakville | KY |
| USOPV | Oakville | WA |
| USOKW | Oakwood | GA |
| USO2A | Oakwood | OH |
| USOW5 | Oakwood | TX |
| USZOV | Oakwood Village | OH |
| USOKH | Oakhurst | NJ |
| USOAK | Oakland | CA |
| USOQA | Oakland | FL |
| USOLI | Oakland | IA |
| USOUF | Oakland | IL |
| USO4K | Oakland | KY |
| USZ2G | Oakland | LA |
| USOBT | Oakland | MD |
| USOKD | Oakland | ME |
| USOQC | Oakland | MS |
| USXKB | Oakland | NJ |
| USKND | Oakland | OR |
| USOV5 | Oakland | PA |
| USDN8 | Oakland | RI |
| USOK3 | Oakland | TX |
| USZOC | Oakland City | IN |
| USO5G | Oakland Gardens | NY |
| USOXK | Oakland Mills | MD |
| USOP2 | Oakland Park, Broward | FL |