| | McLennan County | TX | 48309 | | Waco, TX 47380 | | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=McLennanCounty+TX |
| | McMullen County | TX | 48311 | | | | | nonmetro county (rural) | mining-dependent | https://maps.google.com/?q=McMullenCounty+TX |
| | Madison County | TX | 48313 | | | | | nonmetro county (rural) | federal/state
government-dependent | https://maps.google.com/?q=MadisonCounty+TX |
| | Marion County | TX | 48315 | | | | | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=MarionCounty+TX |
| | Mason County | TX | 48319 | | | | | nonmetro county (rural) | mining-dependent | https://maps.google.com/?q=MasonCounty+TX |
| | Maverick County | TX | 48323 | | Eagle Pass, TX 20580 | | Central | nonmetro county (rural) | federal/state
government-dependent | https://maps.google.com/?q=MaverickCounty+TX |
| | Menard County | TX | 48327 | | | | | nonmetro county (rural) | farm-dependent | https://maps.google.com/?q=MenardCounty+TX |
| | Milam County | TX | 48331 | | | | | nonmetro county (rural) | farm-dependent | https://maps.google.com/?q=MilamCounty+TX |
| | Mills County | TX | 48333 | | | | | nonmetro county (rural) | farm-dependent | https://maps.google.com/?q=MillsCounty+TX |
| | Mitchell County | TX | 48335 | | | | | nonmetro county (rural) | federal/state
government-dependent | https://maps.google.com/?q=MitchellCounty+TX |