| Ontario to Olympia (Washington) | 939.75 mi (1,512.39 km) |
| Ontario to Olympia Heights (Florida) | 2,291.78 mi (3,688.26 km) |
| Ontario to Omaha (Nebraska) | 1,275.93 mi (2,053.41 km) |
| Ontario to On Top of the World Designated Place (Florida) | 2,096.38 mi (3,373.80 km) |
| Ontario to Onalaska (Wisconsin) | 1,563.82 mi (2,516.73 km) |
| Ontario to Oneida (New York) | 2,324.47 mi (3,740.88 km) |
| Ontario to Oneonta (New York) | 2,354.25 mi (3,788.80 km) |
| Ontario to Ontario (Oregon) | 690.83 mi (1,111.78 km) |
| Ontario to Opa-locka (Florida) | 2,291.74 mi (3,688.20 km) |
| Ontario to Opelika (Alabama) | 1,854.91 mi (2,985.19 km) |
| Ontario to Opelousas (Louisiana) | 1,506.60 mi (2,424.64 km) |
| Ontario to Orange (California) | 20.43 mi (32.87 km) |
| Ontario to Orange (Texas) | 1,418.57 mi (2,282.97 km) |
| Ontario to Orange City (Florida) | 2,157.32 mi (3,471.87 km) |
| Ontario to Orangeburg (South Carolina) | 2,099.09 mi (3,378.15 km) |
