| Castle Rock to Olympia Heights (Florida) | 1,702.23 mi (2,739.47 km) |
| Castle Rock to Omaha (Nebraska) | 481.34 mi (774.64 km) |
| Castle Rock to On Top of the World Designated Place (Florida) | 1,465.43 mi (2,358.38 km) |
| Castle Rock to Onalaska (Wisconsin) | 769.35 mi (1,238.14 km) |
| Castle Rock to Oneida (New York) | 1,530.36 mi (2,462.88 km) |
| Castle Rock to Oneonta (New York) | 1,561.56 mi (2,513.09 km) |
| Castle Rock to Ontario (California) | 795.79 mi (1,280.70 km) |
| Castle Rock to Ontario (Oregon) | 702.08 mi (1,129.88 km) |
| Castle Rock to Opa-locka (Florida) | 1,698.52 mi (2,733.50 km) |
| Castle Rock to Opelika (Alabama) | 1,180.03 mi (1,899.08 km) |
| Castle Rock to Opelousas (Louisiana) | 945.45 mi (1,521.55 km) |
| Castle Rock to Orange (California) | 814.84 mi (1,311.35 km) |
| Castle Rock to Orange (Texas) | 896.02 mi (1,442.01 km) |
| Castle Rock to Orange City (Florida) | 1,521.75 mi (2,449.02 km) |
| Castle Rock to Orangeburg (South Carolina) | 1,389.14 mi (2,235.61 km) |
