| Name | What | Region | Country | Lat | Long | Elev ft. | Pop est |
|---|---|---|---|---|---|---|---|
| O'Leary | city | Iowa | United States | 42.71 | -96.06 | 1669 | |
| O'Neill | city | Iowa | United States | 42.61 | -90.89 | 853 | |
| Oakdale | city | Iowa | United States | 41.71 | -91.60 | 830 | |
| Oakfield | city | Iowa | United States | 41.53 | -94.91 | 1669 | |
| Oakland | city | Iowa | United States | 42.58 | -93.44 | 1141 | |
| Oakland | city | Iowa | United States | 41.31 | -95.40 | 1181 | |
| Oakland Acres | city | Iowa | United States | 41.72 | -92.82 | 948 | |
| Oakland Mills | city | Iowa | United States | 40.94 | -91.62 | 830 | |
| Oakley | city | Iowa | United States | 41.10 | -93.37 | 951 | |
| Oakville | city | Iowa | United States | 41.10 | -91.04 | 830 | |
| Oakwood | city | Iowa | United States | 43.01 | -92.78 | 1046 | |
| Oakwood Heights Mobile Home Park | city | Iowa | United States | 41.69 | -93.55 | 921 | |
| Oakwood Station (historical) | city | Iowa | United States | 41.94 | -93.52 | 918 | |
| Oasis | city | Iowa | United States | 41.71 | -91.39 | 839 | |
| Ocheyedan | city | Iowa | United States | 43.42 | -95.53 | 1669 | |
| Odebolt | city | Iowa | United States | 42.31 | -95.25 | 1669 | |
| Oelwein | city | Iowa | United States | 42.67 | -91.91 | 1049 | |
| Ogden | city | Iowa | United States | 42.04 | -94.03 | 1099 | |
| Okoboji | city | Iowa | United States | 43.39 | -95.15 | 1669 | |
| Olaf | city | Iowa | United States | 42.89 | -93.72 | 1249 | |
| Old Balltown | city | Iowa | United States | 42.63 | -90.86 | 997 | |
| Old Orchard Mobile Home Park | city | Iowa | United States | 42.01 | -93.63 | 902 | |
| Old Peru | city | Iowa | United States | 41.24 | -93.95 | 994 | |
| Old Town | city | Iowa | United States | 43.31 | -95.14 | 1669 | |
| Old Tripoli | city | Iowa | United States | 42.83 | -92.27 | 1056 | |
| Olds | city | Iowa | United States | 41.13 | -91.54 | 830 | |
| Olin | city | Iowa | United States | 42.00 | -91.14 | 830 | |
| Olivet | city | Iowa | United States | 41.31 | -92.83 | 843 | |
| Ollie | city | Iowa | United States | 41.20 | -92.09 | 830 | |
| Olmitz | city | Iowa | United States | 41.08 | -93.17 | 921 | |
| Onawa | city | Iowa | United States | 42.03 | -96.10 | 1046 | |
| Onawa Junction | city | Iowa | United States | 42.72 | -95.56 | 1240 | |
| Oneida | city | Iowa | United States | 42.54 | -91.35 | 1033 | |
| Onslow | city | Iowa | United States | 42.11 | -91.02 | 872 | |
| Ontario | city | Iowa | United States | 42.04 | -93.68 | 997 | |
| Oralabor | city | Iowa | United States | 41.70 | -93.59 | 951 | |
| Oran | city | Iowa | United States | 42.70 | -92.07 | 1066 | |
| Orange | city | Iowa | United States | 42.43 | -92.36 | 951 | |
| Orange City | city | Iowa | United States | 43.01 | -96.06 | 1669 | |
| Orchard | city | Iowa | United States | 43.23 | -92.77 | 1076 | |
| Orchard Lane Mobile Home Court | city | Iowa | United States | 42.49 | -91.47 | 912 | |
| Orchard Park Mobile Home Court | city | Iowa | United States | 43.14 | -93.37 | 1220 | |
| Ord | city | Iowa | United States | 41.25 | -94.07 | 1184 | |
| Orient | city | Iowa | United States | 41.20 | -94.41 | 1669 | |
| Orilla | city | Iowa | United States | 41.51 | -93.73 | 928 | |
| Orleans | city | Iowa | United States | 40.73 | -92.66 | 961 | |
| Orleans | city | Iowa | United States | 43.45 | -95.09 | 1669 | |
| Ormanville | city | Iowa | United States | 40.91 | -92.48 | 830 | |
| Orson | city | Iowa | United States | 41.78 | -95.98 | 1040 | |
| Orton | city | Iowa | United States | 41.59 | -95.81 | 1092 | |
| Ortonville | city | Iowa | United States | 41.61 | -93.96 | 1030 | |
| Osage | city | Iowa | United States | 43.28 | -92.81 | 1164 | |
| Osborne | city | Iowa | United States | 42.79 | -91.45 | 830 | |
| Osceola | city | Iowa | United States | 41.03 | -93.77 | 1105 | |
| Osgood | city | Iowa | United States | 43.19 | -94.70 | 1236 | |
| Oskaloosa | city | Iowa | United States | 41.30 | -92.64 | 856 | |
| Ossian | city | Iowa | United States | 43.15 | -91.76 | 1256 | |
| Osterdock | city | Iowa | United States | 42.73 | -91.16 | 830 | |
| Oswalt | city | Iowa | United States | 41.70 | -93.30 | 830 | |
| Otho | city | Iowa | United States | 42.42 | -94.15 | 1118 | |
| Otis | city | Iowa | United States | 41.95 | -91.62 | 830 | |
| Otley | city | Iowa | United States | 41.46 | -93.04 | 849 | |
| Oto | city | Iowa | United States | 42.28 | -95.89 | 1076 | |
| Otranto | city | Iowa | United States | 43.46 | -92.99 | 1118 | |
| Ottawa | city | Iowa | United States | 41.31 | -93.50 | 830 | |
| Ottawa | city | Iowa | United States | 41.03 | -93.59 | 1082 | |
| Otter Creek | city | Iowa | United States | 42.24 | -90.68 | 987 | |
| Otterville | city | Iowa | United States | 42.51 | -91.95 | 948 | |
| Ottosen | city | Iowa | United States | 42.89 | -94.38 | 1141 | |
| Ottumwa | city | Iowa | United States | 41.02 | -92.41 | 830 | |
| Ottumwa Junction | city | Iowa | United States | 41.05 | -92.44 | 830 | |
| Overland Mobile Home Park | city | Iowa | United States | 41.25 | -95.89 | 977 | |
| Ovia | city | Iowa | United States | 40.86 | -93.32 | 1053 | |
| Owasa | city | Iowa | United States | 42.43 | -93.21 | 1118 | |
| Owego | city | Iowa | United States | 42.28 | -96.15 | 1069 | |
| Owen | city | Iowa | United States | 43.04 | -93.08 | 1145 | |
| Oxford | city | Iowa | United States | 41.72 | -91.79 | 830 | |
| Oxford Junction | city | Iowa | United States | 41.98 | -90.96 | 830 | |
| Oxford Mills | city | Iowa | United States | 41.97 | -90.96 | 830 | |
| Oyens | city | Iowa | United States | 42.82 | -96.06 | 1669 | |
| Ozark | city | Iowa | United States | 42.20 | -90.88 | 830 | |
| Ozark (historical) | city | Iowa | United States | 42.16 | -90.87 | 830 |