| Mason City to Olympia Heights (Florida) | 1,405.63 mi (2,262.15 km) |
| Mason City to Omaha (Nebraska) | 195.69 mi (314.94 km) |
| Mason City to On Top of the World Designated Place (Florida) | 1,143.29 mi (1,839.95 km) |
| Mason City to Onalaska (Wisconsin) | 112.13 mi (180.46 km) |
| Mason City to Oneida (New York) | 882.96 mi (1,420.99 km) |
| Mason City to Oneonta (New York) | 918.70 mi (1,478.50 km) |
| Mason City to Ontario (California) | 1,453.39 mi (2,339.00 km) |
| Mason City to Ontario (Oregon) | 1,187.32 mi (1,910.81 km) |
| Mason City to Opa-locka (Florida) | 1,397.36 mi (2,248.84 km) |
| Mason City to Opelika (Alabama) | 839.89 mi (1,351.66 km) |
| Mason City to Opelousas (Louisiana) | 874.36 mi (1,407.15 km) |
| Mason City to Orange (California) | 1,472.61 mi (2,369.94 km) |
| Mason City to Orange (Texas) | 900.55 mi (1,449.29 km) |
| Mason City to Orange City (Florida) | 1,183.59 mi (1,904.81 km) |
| Mason City to Orangeburg (South Carolina) | 942.50 mi (1,516.81 km) |
