| Markham to Olympia Heights (Florida) | 1,174.41 mi (1,890.03 km) |
| Markham to Omaha (Nebraska) | 433.66 mi (697.90 km) |
| Markham to On Top of the World Designated Place (Florida) | 914.88 mi (1,472.36 km) |
| Markham to Onalaska (Wisconsin) | 238.38 mi (383.64 km) |
| Markham to Oneida (New York) | 622.16 mi (1,001.27 km) |
| Markham to Oneonta (New York) | 649.99 mi (1,046.05 km) |
| Markham to Ontario (California) | 1,704.40 mi (2,742.97 km) |
| Markham to Ontario (Oregon) | 1,485.88 mi (2,391.29 km) |
| Markham to Opa-locka (Florida) | 1,164.67 mi (1,874.36 km) |
| Markham to Opelika (Alabama) | 630.55 mi (1,014.77 km) |
| Markham to Opelousas (Louisiana) | 803.23 mi (1,292.68 km) |
| Markham to Orange (California) | 1,722.78 mi (2,772.54 km) |
| Markham to Orange (Texas) | 862.19 mi (1,387.56 km) |
| Markham to Orange City (Florida) | 945.96 mi (1,522.37 km) |
| Markham to Orangeburg (South Carolina) | 672.89 mi (1,082.91 km) |
