Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Marsh (historical) | Locale | 224 | Louisa | 41 06 06 N | 091 21 09 W |
| Marsh Creek | Stream | | Chickasaw | 42 58 07 N | 092 12 16 W |
| Marsh Post Office (historical) | Post Office | 224 | Louisa | 41 06 06 N | 091 21 09 W |
| Marshall (historical) | Populated Place | 333 | Ringgold | 40 43 30 N | 094 19 41 W |
| Marshall Cemetery | Cemetery | 238 | Louisa | 41 08 30 N | 091 19 01 W |
| Marshall Cemetery | Cemetery | 399 | Pocahontas | 42 45 48 N | 094 53 36 W |
| Marshall Center School | Building | 281 | Black Hawk | 42 30 59 N | 092 27 53 W |
| Marshall County | Civil | 290 | Marshall | 42 02 00 N | 093 00 03 W |
| Marshall County Courthouse | Building | 287 | Marshall | 42 02 55 N | 092 54 44 W |
| Marshall County Historical Museum | Building | 287 | Marshall | 42 02 53 N | 092 54 33 W |
| Marshall County Home | Building | 317 | Marshall | 42 00 37 N | 093 03 33 W |
| Marshall County Sheriffs Office | Building | 281 | Marshall | 42 02 45 N | 092 54 35 W |
| Marshall Park | Park | 239 | Dubuque | 42 32 05 N | 090 43 10 W |
| Marshall School | School | 192 | Dubuque | 42 31 21 N | 090 39 24 W |
| Marshalltown | Locale | 270 | Marshall | 42 02 35 N | 092 54 31 W |
| Marshalltown | Populated Place | 287 | Marshall | 42 02 58 N | 092 54 29 W |
| Marshalltown Cemetery | Cemetery | 345 | Ringgold | 40 43 10 N | 094 19 41 W |
| Marshalltown Church of Christ | Church | 274 | Marshall | 42 02 44 N | 092 54 14 W |
| Marshalltown City Hall | Building | 286 | Marshall | 42 03 01 N | 092 54 47 W |
| Marshalltown Colliseum | Building | 286 | Marshall | 42 02 60 N | 092 54 51 W |
| Marshalltown Community College | School | 305 | Marshall | 42 00 05 N | 092 54 31 W |
| Marshalltown Fire Station | Building | 283 | Marshall | 42 02 50 N | 092 54 41 W |
| Marshalltown Foot and Ankle Clinic | Hospital | 279 | Marshall | 42 02 57 N | 092 54 16 W |
| Marshalltown High School | School | 288 | Marshall | 42 01 46 N | 092 54 31 W |
| Marshalltown Medical and Surgical Center | Hospital | 286 | Marshall | 42 02 55 N | 092 54 25 W |
| Marshalltown Medical Clinic | Hospital | 286 | Marshall | 42 02 55 N | 092 54 25 W |
| Marshalltown Municipal Airport | Airport | 296 | Marshall | 42 06 45 N | 092 55 04 W |
| Marshalltown Pediatrics Clinic | Hospital | 286 | Marshall | 42 02 55 N | 092 54 25 W |
| Marshalltown Police Department | Building | 286 | Marshall | 42 03 01 N | 092 54 47 W |
| Marshalltown Post Office | Post Office | 284 | Marshall | 42 02 49 N | 092 54 26 W |
| Marshalltown Public Library | Building | 286 | Marshall | 42 03 01 N | 092 54 47 W |
| Marshalltown Speedway | Locale | 287 | Marshall | 42 01 54 N | 092 53 26 W |
| Marston Hall | Building | 293 | Story | 42 01 36 N | 093 38 59 W |
| Martelle | Populated Place | 277 | Jones | 42 01 18 N | 091 21 36 W |
| Martelle (historical) | Locale | 277 | Jones | 42 01 20 N | 091 21 36 W |
| Martelle Christian Church | Church | 277 | Jones | 42 01 17 N | 091 21 35 W |
| Martelle Community Building | Building | 276 | Jones | 42 01 14 N | 091 21 30 W |
| Martelle Fire Department | Building | 276 | Jones | 42 01 14 N | 091 21 30 W |
| Martelle Lake | Lake | 186 | Allamakee | 43 13 18 N | 091 07 32 W |
| Martelle Library | Building | 274 | Jones | 42 01 12 N | 091 21 35 W |
| Martelle Post Office | Post Office | 276 | Jones | 42 01 18 N | 091 21 35 W |
| Martelle United Methodist Church | Church | 275 | Jones | 42 01 12 N | 091 21 34 W |
| Martensdale | Populated Place | 253 | Warren | 41 22 23 N | 093 44 09 W |
| Martensdale City Hall | Building | 253 | Warren | 41 22 23 N | 093 44 09 W |
| Martensdale Community Church | Church | 253 | Warren | 41 22 23 N | 093 44 09 W |
| Martensdale Elementary School | School | 263 | Warren | 41 22 31 N | 093 44 18 W |
| Martensdale Post Office | Post Office | 253 | Warren | 41 22 23 N | 093 44 09 W |
| Martha Creek | Stream | | Winneshiek | 43 22 46 N | 092 00 19 W |
| Martha Yarns Memorial Beach | Beach | 431 | Dickinson | 43 29 30 N | 095 03 18 W |
| Martin Area County Park | Park | 393 | Cherokee | 42 50 59 N | 095 28 15 W |
| Martin Cemetery | Cemetery | 304 | Appanoose | 40 48 20 N | 092 47 01 W |
| Martin Cemetery | Cemetery | 235 | Linn | 42 00 34 N | 091 31 09 W |
| Martin Cemetery | Cemetery | 321 | Page | 40 38 25 N | 095 19 59 W |
| Martin Cemetery | Cemetery | 208 | Washington | 41 12 00 N | 091 40 01 W |
| Martin Chapel Cemetery | Cemetery | 323 | Mills | 41 03 40 N | 095 48 06 W |
| Martin Creek | Stream | | Linn | 41 59 29 N | 091 30 37 W |
| Martin Creek | Stream | | Scott | 41 45 35 N | 090 27 56 W |
| Martin Lake | Reservoir | 259 | Black Hawk | 42 28 52 N | 092 23 16 W |
| Martin Linn Historical Marker | Park | 256 | Cedar | 41 45 34 N | 091 09 07 W |
| Martin Van Buren School | School | 249 | Linn | 41 57 12 N | 091 42 34 W |
| Martinek Wildlife Area | Park | 370 | Howard | 43 19 38 N | 092 06 24 W |
| Martins (historical) | Locale | 190 | Scott | 41 45 07 N | 090 32 08 W |
| Martinsburg | Populated Place | 245 | Keokuk | 41 10 44 N | 092 15 07 W |
| Martinsburg (historical) | Locale | 247 | Keokuk | 41 10 52 N | 092 15 06 W |
| Martinsburg Cemetery | Cemetery | 237 | Wapello | 41 09 10 N | 092 15 08 W |
| Martinsburg Post Office | Post Office | 245 | Keokuk | 41 10 44 N | 092 15 07 W |
| Martinsburg United Methodist Church | Church | 245 | Keokuk | 41 10 44 N | 092 15 07 W |
| Martinstown | Populated Place | 311 | Appanoose | 40 41 14 N | 092 57 33 W |
| Marvel Creek | Stream | | Adair | 41 18 19 N | 094 19 45 W |
| Mary Benedict Hall | Building | 251 | Dubuque | 42 30 28 N | 090 41 31 W |
| Mary Berry Hall | Building | 293 | Warren | 41 21 50 N | 093 33 51 W |
| Mary Christopher Park | Park | 262 | Winneshiek | 43 18 16 N | 091 46 54 W |
| Mary Frances Hall | Building | 253 | Dubuque | 42 30 38 N | 090 41 27 W |
| Mary Greeley Medical Center | Hospital | 285 | Story | 42 02 01 N | 093 36 43 W |
| Mary Hill | Populated Place | 420 | Cherokee | 42 44 08 N | 095 41 19 W |
| Mary Hill Cemetery | Cemetery | 422 | Cherokee | 42 44 10 N | 095 41 21 W |
| Mary Josita Hall | Building | 254 | Dubuque | 42 30 30 N | 090 41 31 W |
| Mary Winks Park | Park | 324 | Bremer | 42 50 52 N | 092 05 26 W |
| Marybell Post Office (historical) | Post Office | 270 | Polk | 41 34 49 N | 093 21 41 W |
| Marycrest College | School | 220 | Scott | 41 31 50 N | 090 35 54 W |
| Maryhill Visitation Church | Church | 421 | Cherokee | 42 44 09 N | 095 41 20 W |
| Marysville | Locale | 360 | Franklin | 42 40 09 N | 093 11 52 W |
| Marysville | Populated Place | 219 | Marion | 41 10 50 N | 092 56 57 W |
| Marysville (historical) | Populated Place | 222 | Wapello | 41 17 17 N | 092 13 44 W |
| Marysville Bridge | Bridge | 248 | Marion | 41 18 50 N | 093 07 56 W |
| Marysville Cemetery | Cemetery | 262 | Marion | 41 11 11 N | 092 57 21 W |
| Marysville Post Office | Post Office | 219 | Marion | 41 10 50 N | 092 56 57 W |
| Maryville | Populated Place | 351 | Fayette | 42 41 16 N | 091 38 44 W |
| Maskunky Marsh | Park | 210 | Mahaska | 41 18 20 N | 092 31 26 W |
| Mason Cemetery | Cemetery | 226 | Cedar | 41 49 12 N | 091 18 39 W |
| Mason City | Civil | 344 | Cerro Gordo | 43 09 05 N | 093 11 55 W |
| Mason City | Populated Place | 344 | Cerro Gordo | 43 09 13 N | 093 12 04 W |
| Mason City Baptist Church | Church | 360 | Cerro Gordo | 43 08 06 N | 093 14 30 W |
| Mason City Campground | Locale | 329 | Cerro Gordo | 43 09 15 N | 093 09 56 W |
| Mason City Clinic | Hospital | 345 | Cerro Gordo | 43 08 59 N | 093 12 50 W |
| Mason City Country Club | Locale | 355 | Cerro Gordo | 43 07 50 N | 093 14 56 W |
| Mason City Covenant Church | Church | 336 | Cerro Gordo | 43 08 38 N | 093 10 37 W |
| Mason City Fire Department | Building | 340 | Cerro Gordo | 43 08 51 N | 093 12 24 W |
| Mason City Hall | Building | 344 | Cerro Gordo | 43 09 11 N | 093 12 06 W |
| Mason City High School | School | 329 | Cerro Gordo | 43 08 56 N | 093 10 01 W |
| Mason City Junction | Populated Place | 360 | Cerro Gordo | 43 07 07 N | 093 11 21 W |
| Mason City Municipal Airport | Airport | 364 | Cerro Gordo | 43 09 28 N | 093 19 52 W |
| Mason City Police Department | Building | 343 | Cerro Gordo | 43 09 04 N | 093 11 48 W |
| Mason City Post Office | Post Office | 344 | Cerro Gordo | 43 09 15 N | 093 11 57 W |
| Mason City Public Library | Building | 343 | Cerro Gordo | 43 08 58 N | 093 11 51 W |
| Mason Creek | Stream | | Cedar | 41 49 03 N | 091 17 34 W |
| Mason Creek | Stream | | Cerro Gordo | 43 08 09 N | 093 08 19 W |
| Mason Creek | Stream | | Guthrie | 41 39 47 N | 094 29 46 W |
| Mason Creek | Stream | | Scott | 41 45 25 N | 090 37 26 W |
| Mason Park | Park | 322 | Webster | 42 29 55 N | 094 11 00 W |