Public Sites
| State | County | Name |
|---|---|---|
| Iowa | Monona | Oldham Recreation Area |
| Iowa | Henry | Olds |
| Iowa | Jones | Olin Access Wildlife Management Area |
| Iowa | Linn | Oliphant Cemetery |
| Iowa | Monona | Onawa |
| Iowa | Monona | Onawa Rest Stop on I29 |
| Iowa | Boone | Onion Creek Area |
| Iowa | Story | Ontario |
| Iowa | Sioux | Orange City |
| Iowa | Sioux | Orange City Slough |
| Florida | Sarasota | Orange Hammock Wildlife Area |
| Iowa | Adair | Orient |
| Missouri | Camden | Osage Beach |
| Iowa | Clayton | Osborne Outdoor Education Center Park |
| Iowa | Clayton | Osborne Pond |
| Florida | Sarasota | Oscar Scherer State Park |
| Iowa | Osceola | Osceola County |
| Iowa | Mahaska | Oskaloosa |
| Iowa | Allamakee | Osterholm Site |
| Iowa | Webster | Otho |
| Iowa | Woodbury | Oto |
| Iowa | Mitchell | Otranto Park |
| Iowa | Mitchell | Otranto Wildlife Area |
| Ohio | Ottawa | Ottawa National Wildlife Refuge |
| Iowa | Osceola | Otter Creek @ 190th Street |