1850 Atlas
| Name | What | Place | Pop | Other |
| Mobile | City | Mobile Co, AL | 20,515 | seat of justice, on Mobile bay |
| Mobley Pond | PO | Seriven Co, GA | ||
| Mockville | PV | Davie Co, NC | seat of justice | |
| Modena | PO | Plattekill twp, Ulster Co, NY | ||
| Modest Town | PV | Accomac Co, VA | ||
| Modrell's Point | PO | Coles Co, IL | ||
| Moffett's Store | PO | New Lebanon twp, Columbia Co, NY | ||
| Moffettsville | PV | Anderson dist, SC | ||
| Moffitt's Mill | PO | Randolph Co, NC | ||
| Mogadore | PO | Summit Co, OH | ||
| Mohawk | PV | German Flats twp, Herkimer Co, NY | water by Mohawk river & Erie canal | |
| Mohawk | T | Montgomery Co, NY | 3,095 | water by Mohawk river |
| Mohawk Valley | PO | Coshocton Co, OH | ||
| Mohican | PT | Ashland Co, OH | 1,775 | |
| Mohrsville | PO | Berks Co, PA | ||
| Moira | PT | Franklin Co, NY | 1,340 | water by Little Salmon river |
| Mikelumne Hill | PO | Calaveras Co, CA | ||
| Moline | PO | Rock Island Co, IL | ||
| Molino | PO | Tippah Co, MS | ||
| Molino | PO | Lincoln Co, TN | ||
| Molino | PO | Randolph Co, AR | ||
| Mollihorn | PO | Newberry dist, SC | ||
| Molltown | PV | Berks Co, PA | ||
| Momence | PO | Will Co, IL | ||
| Monagan | PT | St Clair Co, MO | ||
| Monches | PO | Waukesha Co, WI | ||
| Monclova | PO | Lucas Co, OH | ||
| Moneek | PO | Winneshiek Co, IA | ||
| Monday Creek | T | Perry Co, OH | 1,124 | |
| Money Creek | PO | McLean Co, IL | ||
| Mongaugon | T | Wayne Co, MI | 984 | |
| Mongaup | PO | Sullivan Co, NY | ||
| Mongaup Valley | PO | Sullivan Co, NY | ||
| Mongoquinong | PO | La Grange Co, IN | ||
| Moniteau | T | Cole Co, MO | ||
| Moniteau | T | Cooper Co, MO | ||
| Moniteau | T | Howard Co, MO | ||
| Monk's Corners | PO | Charleston dist, SC | ||
| Monk's Store | PO | Sampson Co, NC | ||
| Monkton | PT | Addison Co, VT | 1,246 | water by tributaries of Lewis creek |
| Monkton Mills | PO | Baltimore Co, MD | ||
| Monmouth | PT | Kennebec Co, ME | 1,925 | water by head waters of Cobesseconte river |
| Monmouth | PV | Adams Co, IN | water by St Mary's river | |
| Monmouth | PV, CH | Warren Co, IL | seat of justice | |
| Monohan | T | York Co, PA | 880 | |
| Monon | PO | White Co, IN | ||
| Monona | PO | Clayton Co, IA | ||
| Monongahela | T | Greene Co, PA | 1,153 | water by Whitey creek |
| Monongahela | City, PO | Fallowfield twp, Washington Co, PA | 977 | |
| Monoquet | PO | Kosciusko Co, IN | ||
| Monreath | PO | Shelby Co, TN | ||
| Monroe | PT | Waldo Co, ME | 1,606 | water by Marsh river |
| Monroe | T | Washington Co, VT | 1,335 | water by tributaries of Onion or Winooski & Lamoille rivers |
| Monroe | PT | Franklin Co, MA | 654 | water by Deerfield river |
| Monroe | PT | Franklin Co, CT | 1,319 | |
| Monroe | PT | Orange Co, NY | 4,280 | water by Ramapo river |
| Monroe | PV | Hardiston twp, Sussex Co, NJ | ||
| Monroe | T | Middlesex Co, NJ | 3,001 | |
| Monroe | T | Bradford Co, PA | 1436 | |
| Monroe | V | Durham twp, Bucks Co, PA | ||
| Monroe | T | Cumberland Co, PA | 1,772 | water by Yellow Breech's creek |
| Monroe | T | Luzerne Co, PA | 681 | |
| Monroe | T | Armstrong Co, PA | 775 | |
| Monroe | PV, CH | Walton Co, GA | seat of justice, water by Ocumlgee river | |
| Monroe | PV | Wachita parish, LA | water by Wachita river, at the head of steam navigation | |
| Monroe | PV | Overton Co, TN | water by a tributary of Obie's river | |
| Monroe | PV | Hart Co, KY | water by Little Barren river | |
| Monroe | PV | Lemon twp, Butler Co, OH | 206 | |
| Monroe | T | Adams Co, OH | 1,191 | water by Ohio rivers |
| Monroe | T | Ashtabula Co, OH | 1,587 | |
| Monroe | PT | Butler Co, OH | ||
| Monroe | T | Carroll Co, OH | 1,117 | |
| Monroe | T | Clermont Co, OH | 1,897 | |
| Monroe | T | Coshocton Co, OH | 760 | |
| Monroe | T | Darke Co, OH | 918 | |
| Monroe | T | Guernsey Co, OH | 1,076 | |
| Monroe | T | Harrison Co, OH | 1,154 | |
| Monroe | T | Holmes Co, OH | 966 | |
| Monroe | T | Knox Co, OH | 1,324 | water by Schenck's creek |
| Monroe | T | Licking Co, OH | 1,089 | |
| Monroe | T | Logan Co, OH | 1,435 | |
| Monroe | T | Madison Co, OH | 403 | |
| Monroe | T | Miami Co, OH | 2,035 | |
| Monroe | T | Muskingum Co, OH | 977 | |
| Monroe | T | Perry Co, OH | 1,429 | |
| Monroe | T | Preble Co, OH | 1,343 | |
| Monroe | T | Pickaway Co, OH | 1,637 | |
| Monroe | T | Richland Co, OH | 1,719 | water by Mohiccan creek |
| Monroe | T | Putnam Co, OH | ||
| Monroe | T | Grant Co, IN | 777 | |
| Monroe | T | Putnam Co, IN | 1,089 | |
| Monroe | T | Washington Co, IN | 1,476 | |
| Monroe | City | Monroe Co, MI | 2,813 | seat of justice, water by Raisin river |
| Monroe | PV, CH | Greene Co, WI | seat of justice, water by tributary of Pickatonokee river | |
| Monroe | T | Ogle Co, IL | 413 | |
| Monroe | T | Lincoln Co, MO | ||
| Monroe | T | Livingston Co, MO | ||
| Monroe | T | Mississippi Co, AR | 652 | |
| Monroe | T | Sevier Co, AR | 335 | |
| Monroe | PO | Perry Co, MS | ||
| Monroe | PO | Tippecanoe Co, IN | ||
| Monroe | PO | Bedford Co, PA | ||
| Monroe | PV, CH | Union Co, NC | seat of justice | |
| Monroe Centre | PO | Monroe twp, Waldo Co, ME | ||
| Monroe Centre | PO | Monroe twp, Ashtabula Co, OH | ||
| Monroe Mills | PO | Knox Co, OH | ||
| Monroe Works | PV | Monroe twp, Orange Co, NY | ||
| Monroeton | PV | Monroe twp, Bradford Co, PA | ||
| Monroeton | PV | Rockingham Co, NC | ||
| Monroeville | PV, CH | Monroe Co, AL | seat of justice, water by tributary of Limestone creek | |
| Monroeville | PV | Ridefield twp, Huron Co, OH | water by Huron river | |
| Monroeville | PO | Alleghany Co, PA | ||
| Monroeville | PV, CH | Colosi Co, CA | seat of justice | |
| Monrovia | PV | Morgan Co, IN | ||
| Monrovia | PV | Frederick Co, MD |