| Ontario to Odenton (Maryland) | 2,277.82 mi (3,665.79 km) |
| Ontario to Odessa (Texas) | 896.37 mi (1,442.56 km) |
| Ontario to Ogden (Utah) | 584.38 mi (940.46 km) |
| Ontario to Oildale (California) | 125.55 mi (202.05 km) |
| Ontario to Ojus (Florida) | 2,295.60 mi (3,694.41 km) |
| Ontario to Okemos (Michigan) | 1,881.00 mi (3,027.18 km) |
| Ontario to Oklahoma City (Oklahoma) | 1,142.91 mi (1,839.33 km) |
| Ontario to Okmulgee (Oklahoma) | 1,227.43 mi (1,975.35 km) |
| Ontario to Olathe (Kansas) | 1,305.86 mi (2,101.58 km) |
| Ontario to Old Jamestown (Missouri) | 1,548.28 mi (2,491.72 km) |
| Ontario to Oldsmar (Florida) | 2,098.59 mi (3,377.35 km) |
| Ontario to Olean (New York) | 2,181.85 mi (3,511.34 km) |
| Ontario to Olive Branch (Mississippi) | 1,576.88 mi (2,537.74 km) |
| Ontario to Olivehurst (California) | 411.40 mi (662.08 km) |
| Ontario to Olney (Maryland) | 2,257.23 mi (3,632.65 km) |
