Public Sites
| State | County | Name |
|---|---|---|
| Iowa | Clarke | Clarke County |
| Iowa | Butler | Clarksville |
| Iowa | Clay | Clay County |
| Minnesota | Clay | Clay County |
| Iowa | Butler | Clay Prairie State Preserve |
| Iowa | Cerro Gordo | Claybanks Forest State Preserve East |
| Iowa | Cerro Gordo | Claybanks Forest State Preserve West |
| Iowa | Clayton | Clayton |
| Iowa | Clayton | Clayton County |
| Iowa | Clayton | Clayton Road - Buck Creek - Trout |
| Iowa | Jasper | Clear Creek @ F24 |
| Iowa | Johnson | Clear Creek @ S Park Rd |
| Iowa | Allamakee | Clear Creek Fen |
| Iowa | Johnson | Clear Creek Trail-Coralville Segment |
| Iowa | Allamakee | Clear Creek Wildlife Management Area |
| Iowa | Cerro Gordo | Clear Lake |
| Iowa | Davis | Clearview Prairie |
| Iowa | Washington | Clemmons Creek Wildlife and Recreation Area |
| Iowa | Fayette | Clermont |
| Ohio | Cuyahoga | Cleveland Waterfront |
| Iowa | Hardin | Cleves |
| North Carolina | Swain | Clingman's Dome |
| Iowa | Clinton | Clinton County |
| Iowa | Boone | Clover Woods Camp and Retreat Center |
| Iowa | Jackson | Codfish Hollow Prairie |