| Code | Name | Region |
|---|---|---|
| USMDO | Middleton Island | AK |
| USDLW | Middletown | CA |
| USXIN | Middletown | CT |
| USMIU | Middletown | DE |
| USM76 | Middletown | IA |
| USJDD | Middletown | IN |
| USM44 | Middletown | MD |
| USILQ | Middletown | MO |
| USMIJ | Middletown | NJ |
| USMIY | Middletown | NY |
| USMWO | Middletown | OH |
| USUQT | Middletown | PA |
| USYMT | Middletown | RI |
| USXXH | Middlebranch | OH |
| USMB8 | Middleburg | FL |
| USHQ4 | Middleburg | NC |
| USLRG | Middleburg | PA |
| USD7D | Middleburg | TN |
| USMG9 | Middleburg | VA |
| USMBV | Middleburg Heights | OH |
| USDBU | Middleburg, Logan | OH |
| USM2D | Middlebury | CT |
| USMDU | Middlebury | IN |
| USMBU | Middlebury | VT |
| USURY | Middlebury Center | PA |
| USXXD | Middlefield | CT |
| US3DF | Middlefield | MA |
| USQMI | Middlefield | OH |
| USM3P | Middleport | NY |
| USMIP | Middleport | OH |
| USMBR | Middlesboro | KY |
| USIDD | Middlesex | NC |
| USMIS | Middlesex | NJ |
| USICA | Micanopy | FL |
| USM3V | Micaville | NC |
| USMI7 | Michael | IL |
| USMG8 | Michigamme | MI |
| USIGX | Michigan | ND |
| USMNC | Michigan Center | MI |
| USMGC | Michigan City | IN |
| USKMH | Michigantown | IN |
| USXIQ | Mickleton | NJ |
| USIQO | Mico | TX |
| USMI9 | Midas | NV |
| USIFH | Middle Falls | NY |
| USMGL | Middle Granville | NY |
| USM9G | Middle Grove | NY |
| USZIX | Middle Island | NY |
| US7MP | Middle Point | OH |
| USMDV | Middle River | MD |