| Code | Name | Region |
|---|---|---|
| USMYK | May Creek | AK |
| USMYQ | Maybrook | NY |
| USM9Y | Mayer | AZ |
| USYMM | Mayer | MN |
| USM2Y | Mayersville | MS |
| USYEI | Mayetta | KS |
| USMY8 | Mayfield | ID |
| USMAY | Mayfield | KY |
| USM9F | Mayfield | OH |
| USMFP | Mayfield | PA |
| USM3H | Mayfield Heights | OH |
| USMF7 | Mayfield, Butler | OH |
| USAYF | Mayfield, Cuyahoga | OH |
| US6KT | Mattawamkeag | ME |
| USMNW | Mattawan | MI |
| USAES | Matteson | IL |
| USH33 | Matthews | IN |
| USMW9 | Matthews | MO |
| USMUA | Matthews | NC |
| USXUK | Mattituck | NY |
| USMTO | Mattoon | IL |
| USKMA | Mattoon | WI |
| USMTD | Mattydale | NY |
| USMP2 | Mauckport | IN |
| USMAU | Mauldin | SC |
| USMMY | Maumee | OH |
| USMLE | Maumelle | AR |
| USUCW | Mauricetown | NJ |
| USNJS | Mauriceville | TX |
| USYCT | Maury City | TN |
| USTSX | Mauston | WI |
| USMXM | Max Meadows | VA |
| USMXE | Maxton | NC |
| USAQU | Massapequa | NY |
| USMSS | Massena | NY |
| USQMZ | Massey | MD |
| USXJF | Massillon | OH |
| USZTC | Mastic | NY |
| USMZ7 | Mastic Beach | NY |
| USMSU | Masury | OH |
| USMD2 | Matador | TX |
| USMGI | Matagorda Island | TX |
| USMTU | Matanuska | AK |
| USTAW | Matawan | NJ |
| USM9W | Matewan | WV |
| USTHC | Mather | CA |
| USMJW | Mathews | LA |
| USZMI | Mathis | TX |
| USMI6 | Mathiston | MS |
| USM4T | Matson | MO |