| Monroe to Olympia Heights (Florida) | 849.03 mi (1,366.38 km) |
| Monroe to Omaha (Nebraska) | 642.66 mi (1,034.27 km) |
| Monroe to On Top of the World Designated Place (Florida) | 626.68 mi (1,008.55 km) |
| Monroe to Onalaska (Wisconsin) | 786.98 mi (1,266.53 km) |
| Monroe to Oneida (New York) | 1,151.92 mi (1,853.83 km) |
| Monroe to Oneonta (New York) | 1,154.43 mi (1,857.88 km) |
| Monroe to Ontario (California) | 1,474.55 mi (2,373.06 km) |
| Monroe to Ontario (Oregon) | 1,558.04 mi (2,507.43 km) |
| Monroe to Opa-locka (Florida) | 846.13 mi (1,361.72 km) |
| Monroe to Opelika (Alabama) | 390.13 mi (627.85 km) |
| Monroe to Opelousas (Louisiana) | 137.72 mi (221.65 km) |
| Monroe to Orange (California) | 1,487.85 mi (2,394.46 km) |
| Monroe to Orange (Texas) | 193.06 mi (310.70 km) |
| Monroe to Orange City (Florida) | 686.56 mi (1,104.91 km) |
| Monroe to Orangeburg (South Carolina) | 652.71 mi (1,050.44 km) |
