| Delaware to Olympia Heights (Florida) | 1,018.33 mi (1,638.84 km) |
| Delaware to Omaha (Nebraska) | 681.81 mi (1,097.26 km) |
| Delaware to On Top of the World Designated Place (Florida) | 773.70 mi (1,245.15 km) |
| Delaware to Onalaska (Wisconsin) | 485.37 mi (781.12 km) |
| Delaware to Oneida (New York) | 428.14 mi (689.03 km) |
| Delaware to Oneonta (New York) | 441.23 mi (710.08 km) |
| Delaware to Ontario (California) | 1,936.80 mi (3,116.98 km) |
| Delaware to Ontario (Oregon) | 1,743.06 mi (2,805.19 km) |
| Delaware to Opa-locka (Florida) | 1,007.08 mi (1,620.74 km) |
| Delaware to Opelika (Alabama) | 542.02 mi (872.29 km) |
| Delaware to Opelousas (Louisiana) | 842.80 mi (1,356.36 km) |
| Delaware to Orange (California) | 1,954.57 mi (3,145.58 km) |
| Delaware to Orange (Texas) | 924.28 mi (1,487.49 km) |
| Delaware to Orange City (Florida) | 790.73 mi (1,272.55 km) |
| Delaware to Orangeburg (South Carolina) | 484.84 mi (780.28 km) |
