| Iowa |
| Oakdale | Olds | Orient | Ottosen |
| Oakland | Olin | Osage | Ottumwa |
| Oakville | Ollie | Osceola | Oxford |
| Ocheyedan | Onawa | Oskaloosa | Oxford Junction |
| Odebolt | Onslow | Ossian | Oyens |
| Oelwein | Oran | Otho | |
| Ogden | Orange City | Otley | |
| Okoboji | Orchard | Oto |
| Popular towns & cities |
| Ames | Cedar Rapids | Des Moines | Mason City |
| Ankeny | Clinton | Dubuque | Sioux City |
| Bettendorf | Coralville | Fort Dodge | Urbandale |
| Burlington | Council Bluffs | Iowa City | Waterloo |
| Cedar Falls | Davenport | Johnston | West Des Moines |
