Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Mardan Mobile Home Court | Populated Place | 215 | Henry | 40 57 07 N | 091 33 51 W |
| Mardean Park | Park | 305 | Story | 42 00 10 N | 093 26 47 W |
| Marena | Locale | 373 | Ringgold | 40 50 30 N | 094 23 46 W |
| Marena Post Office (historical) | Post Office | 356 | Ringgold | 40 50 60 N | 094 24 32 W |
| Marengo | Locale | 226 | Iowa | 41 47 34 N | 092 04 11 W |
| Marengo | Populated Place | 225 | Iowa | 41 47 53 N | 092 04 15 W |
| Marengo City Hall | Building | 223 | Iowa | 41 48 04 N | 092 04 07 W |
| Marengo City Lions Park | Park | 224 | Iowa | 41 48 00 N | 092 04 10 W |
| Marengo Elevator Company Elevator | Locale | 226 | Iowa | 41 47 34 N | 092 04 11 W |
| Marengo Medical Center | Hospital | 225 | Iowa | 41 48 09 N | 092 04 21 W |
| Marengo Memorial Hospital | Hospital | 224 | Iowa | 41 48 17 N | 092 04 23 W |
| Marengo Post Office | Post Office | 225 | Iowa | 41 47 59 N | 092 04 17 W |
| Margaret MacNider Park | Park | 331 | Cerro Gordo | 43 09 30 N | 093 11 11 W |
| Margaretta Carey Elementary School | School | 286 | Bremer | 42 44 06 N | 092 28 29 W |
| Marge Dodd Stage | Building | 247 | Wapello | 41 02 45 N | 092 23 41 W |
| Margo Frankel Woods State Park | Park | 272 | Polk | 41 40 22 N | 093 37 00 W |
| Maria Hladik Roadside Park | Park | 295 | Tama | 42 05 13 N | 092 34 51 W |
| Marian Grotto | Park | 214 | Scott | 41 32 21 N | 090 34 52 W |
| Marian Health Center Heliport | Airport | 342 | Woodbury | 42 29 45 N | 096 24 06 W |
| Marian Health Center Number 2 Heliport | Airport | 342 | Woodbury | 42 29 45 N | 096 24 06 W |
| Marian Health Center Number 3 Heliport | Airport | 379 | Woodbury | 42 30 51 N | 096 23 51 W |
| Marian Health Center School of Medical Technology | School | 360 | Woodbury | 42 29 49 N | 096 24 01 W |
| Marian Health Center School of Radiologic Technology | School | 360 | Woodbury | 42 29 49 N | 096 24 01 W |
| Marian Home and Village Nursing Home | Hospital | 338 | Webster | 42 30 45 N | 094 09 56 W |
| Marietta | Populated Place | 272 | Marshall | 42 04 59 N | 093 00 02 W |
| Marietta (historical) | Locale | 272 | Marshall | 42 04 59 N | 093 00 02 W |
| Marietta Cemetery | Cemetery | 288 | Marshall | 42 04 03 N | 093 00 04 W |
| Marietta Park | Park | | Scott | 41 27 35 N | 090 42 59 W |
| Marietta Post Office (historical) | Post Office | 272 | Marshall | 42 04 59 N | 093 00 02 W |
| Marietta Sand Prairie State Preserve | Park | 289 | Marshall | 42 05 35 N | 093 02 21 W |
| Marilie Educational Forest Reserve Wildlife Area | Park | 364 | Winneshiek | 43 10 15 N | 091 37 06 W |
| Marion | Locale | 260 | Linn | 42 02 00 N | 091 35 51 W |
| Marion | Populated Place | 259 | Linn | 42 02 03 N | 091 35 52 W |
| Marion Airport | Airport | 262 | Linn | 42 01 52 N | 091 31 46 W |
| Marion Avenue Baptist Church | Church | 230 | Washington | 41 17 52 N | 091 41 36 W |
| Marion Behavioral Medicine Center | Hospital | 360 | Woodbury | 42 29 49 N | 096 24 01 W |
| Marion Carnegie Library | Building | 257 | Linn | 42 01 54 N | 091 35 56 W |
| Marion Center Cemetery | Cemetery | 384 | Franklin | 42 46 26 N | 093 19 05 W |
| Marion Christian Church | Church | 244 | Linn | 42 02 37 N | 091 35 56 W |
| Marion City Hall | Building | 258 | Linn | 42 02 03 N | 091 35 56 W |
| Marion City Number Four School (historical) | School | 290 | Hamilton | 42 20 26 N | 093 53 24 W |
| Marion City Police Dapartment | Building | 260 | Linn | 42 02 06 N | 091 34 13 W |
| Marion County | Civil | 267 | Marion | 41 20 00 N | 093 06 01 W |
| Marion County Chiropractic Center | Hospital | 289 | Marion | 41 13 25 N | 093 14 31 W |
| Marion County Courthouse | Building | 279 | Marion | 41 19 07 N | 093 05 50 W |
| Marion County Fairground | Locale | 280 | Marion | 41 19 35 N | 093 06 43 W |
| Marion County Historical Village | Locale | 275 | Marion | 41 18 58 N | 093 07 11 W |
| Marion County Park | Park | 249 | Marion | 41 18 51 N | 093 07 34 W |
| Marion County Sheriff Department | Building | 278 | Marion | 41 19 07 N | 093 05 53 W |
| Marion Family Practice Center | Hospital | 257 | Linn | 42 02 17 N | 091 34 28 W |
| Marion Fire Station One | Building | 250 | Linn | 42 02 04 N | 091 36 12 W |
| Marion Football Field | Park | 239 | Linn | 42 01 44 N | 091 36 32 W |
| Marion Free Methodist Church | Church | 245 | Keokuk | 41 19 22 N | 092 19 49 W |
| Marion Free Methodist Church | Church | 253 | Linn | 42 02 51 N | 091 35 02 W |
| Marion G Crandell State Historical Marker | Park | 198 | Scott | 41 32 50 N | 090 33 10 W |
| Marion Gospel Hall | Church | 249 | Linn | 42 01 13 N | 091 36 10 W |
| Marion Health Center | Hospital | 360 | Woodbury | 42 29 49 N | 096 24 01 W |
| Marion Heights Shopping Center | Locale | 247 | Linn | 42 01 10 N | 091 35 52 W |
| Marion High School | School | 261 | Linn | 42 01 24 N | 091 35 31 W |
| Marion Lutheran Cemetery | Cemetery | 337 | Clayton | 42 58 15 N | 091 30 47 W |
| Marion Mobile Home Park | Populated Place | 254 | Linn | 42 01 60 N | 091 34 11 W |
| Marion Park | Park | 377 | Cerro Gordo | 43 08 20 N | 093 22 18 W |
| Marion Post Office | Post Office | 256 | Linn | 42 01 55 N | 091 35 51 W |
| Marion School | School | 286 | Marion | 41 10 32 N | 093 15 11 W |
| Marion Townhall | Building | 285 | Clayton | 42 57 19 N | 091 32 55 W |
| Marion Township Fire Station | Building | 302 | Marshall | 42 06 06 N | 092 49 14 W |
| Marion United Pentecostal Church | Church | 259 | Linn | 42 02 02 N | 091 35 54 W |
| Mariposa County Park | Park | 288 | Jasper | 41 46 48 N | 092 58 01 W |
| Mark | Populated Place | 281 | Davis | 40 39 37 N | 092 30 42 W |
| Mark and Sadie Bishop Conservation Area | Park | 329 | Hamilton | 42 30 25 N | 093 46 21 W |
| Mark Church | Church | 274 | Davis | 40 39 39 N | 092 30 16 W |
| Mark N Morris Bridge | Bridge | 174 | Clinton | 41 52 07 N | 090 10 17 W |
| Mark Post Office (historical) | Post Office | 281 | Davis | 40 39 37 N | 092 30 42 W |
| Mark Twain National Wildlife Refuge | Park | 165 | Louisa | 41 17 02 N | 091 06 14 W |
| Mark Twain Overlook | Locale | 183 | Muscatine | 41 25 37 N | 091 02 02 W |
| Mark Twain School | School | 221 | Johnson | 41 38 35 N | 091 30 56 W |
| Mark Twain School | School | 195 | Scott | 41 32 15 N | 090 30 30 W |
| Market Place Branch Library | Building | 344 | Woodbury | 42 31 14 N | 096 25 10 W |
| Market Place Mall | Locale | 345 | Woodbury | 42 31 21 N | 096 25 10 W |
| Markham Family Dental Associates Center | Hospital | 402 | Shelby | 41 39 04 N | 095 20 21 W |
| Markhams Pond | Lake | 356 | Mitchell | 43 28 42 N | 093 00 25 W |
| Marks Branch | Stream | | Decatur | 40 34 37 N | 093 40 36 W |
| Marks Branch | Stream | 322 | Decatur | 40 35 01 N | 093 44 13 W |
| Marne | Populated Place | 386 | Cass | 41 27 05 N | 095 06 41 W |
| Marne (historical) | Locale | 365 | Cass | 41 26 52 N | 095 06 41 W |
| Marne City Fire Department | Building | 376 | Cass | 41 26 56 N | 095 06 41 W |
| Marne Post Office | Post Office | 376 | Cass | 41 26 56 N | 095 06 41 W |
| Marne Town Hall | Building | 376 | Cass | 41 26 56 N | 095 06 41 W |
| Marnie Simons Elementary School | School | 287 | Fremont | 40 36 58 N | 095 39 09 W |
| Marquette | Locale | 191 | Clayton | 43 02 40 N | 091 10 41 W |
| Marquette | Populated Place | 191 | Clayton | 43 02 40 N | 091 10 41 W |
| Marquette City Hall | Building | 191 | Clayton | 43 02 40 N | 091 10 41 W |
| Marquette City Park | Park | 201 | Clayton | 43 02 38 N | 091 10 45 W |
| Marquette Fire Department | Building | 191 | Clayton | 43 02 40 N | 091 10 41 W |
| Marquette High School | School | 196 | Jackson | 42 15 35 N | 090 25 44 W |
| Marquette Intermediate School | School | 218 | Lee | 40 46 09 N | 091 31 05 W |
| Marquette Post Office | Post Office | 191 | Clayton | 43 02 40 N | 091 10 41 W |
| Marquette School | School | 236 | Lee | 40 42 54 N | 091 27 11 W |
| Marquette School | School | 218 | Lee | 40 47 01 N | 091 36 11 W |
| Marquis Hall | Building | 230 | Linn | 41 59 11 N | 091 39 26 W |
| Marquisville | Populated Place | 284 | Polk | 41 39 24 N | 093 36 03 W |
| Marquisville Post Office (historical) | Post Office | 284 | Polk | 41 39 24 N | 093 36 03 W |
| Marquisville United Methodist Church | Church | 284 | Polk | 41 39 28 N | 093 36 00 W |
| Marr Park | Park | 226 | Washington | 41 17 18 N | 091 34 44 W |
| Marrowbone Creek | Stream | | Carroll | 42 10 06 N | 094 43 04 W |
| Mars Hill Cemetery | Cemetery | 241 | Wapello | 40 53 57 N | 092 21 27 W |
| Mars Hill Church | Church | 240 | Wapello | 40 53 58 N | 092 21 27 W |
| Marsdenville (historical) | Locale | 302 | Appanoose | 40 44 15 N | 093 00 24 W |
| Marsdenville Post Office (historical) | Post Office | 302 | Appanoose | 40 44 15 N | 093 00 24 W |
| Marsh | Populated Place | 224 | Louisa | 41 06 06 N | 091 21 09 W |