| Ontario to Oswego (Illinois) | 1,672.21 mi (2,691.16 km) |
| Ontario to Oswego (New York) | 2,283.15 mi (3,674.37 km) |
| Ontario to Otsego (Minnesota) | 1,484.62 mi (2,389.27 km) |
| Ontario to Ottawa (Illinois) | 1,643.80 mi (2,645.44 km) |
| Ontario to Ottawa (Kansas) | 1,279.58 mi (2,059.28 km) |
| Ontario to Ottumwa (Iowa) | 1,455.79 mi (2,342.88 km) |
| Ontario to Overland (Missouri) | 1,543.11 mi (2,483.40 km) |
| Ontario to Overland Park (Kansas) | 1,312.98 mi (2,113.04 km) |
| Ontario to Overlea (Maryland) | 2,285.79 mi (3,678.62 km) |
| Ontario to Oviedo (Florida) | 2,169.32 mi (3,491.19 km) |
| Ontario to Owasso (Oklahoma) | 1,237.09 mi (1,990.90 km) |
| Ontario to Owatonna (Minnesota) | 1,472.70 mi (2,370.08 km) |
| Ontario to Owensboro (Kentucky) | 1,717.97 mi (2,764.80 km) |
| Ontario to Owings Mills (Maryland) | 2,270.98 mi (3,654.79 km) |
| Ontario to Owosso (Michigan) | 1,895.57 mi (3,050.63 km) |
