| Duncan to Olympia Heights (Florida) | 1,211.79 mi (1,950.19 km) |
| Duncan to Omaha (Nebraska) | 475.44 mi (765.15 km) |
| Duncan to On Top of the World Designated Place (Florida) | 990.30 mi (1,593.73 km) |
| Duncan to Onalaska (Wisconsin) | 738.50 mi (1,188.50 km) |
| Duncan to Oneida (New York) | 1,330.10 mi (2,140.58 km) |
| Duncan to Oneonta (New York) | 1,345.89 mi (2,166.01 km) |
| Duncan to Ontario (California) | 1,122.46 mi (1,806.43 km) |
| Duncan to Ontario (Oregon) | 1,207.03 mi (1,942.52 km) |
| Duncan to Opa-locka (Florida) | 1,209.31 mi (1,946.19 km) |
| Duncan to Opelika (Alabama) | 733.00 mi (1,179.65 km) |
| Duncan to Opelousas (Louisiana) | 438.83 mi (706.22 km) |
| Duncan to Orange (California) | 1,136.89 mi (1,829.66 km) |
| Duncan to Orange (Texas) | 390.03 mi (627.69 km) |
| Duncan to Orange City (Florida) | 1,049.68 mi (1,689.30 km) |
| Duncan to Orangeburg (South Carolina) | 978.22 mi (1,574.29 km) |
