| Middle River to Olympia Heights (Florida) | 967.96 mi (1,557.78 km) |
| Middle River to Omaha (Nebraska) | 1,040.44 mi (1,674.42 km) |
| Middle River to On Top of the World Designated Place (Florida) | 782.14 mi (1,258.73 km) |
| Middle River to Onalaska (Wisconsin) | 824.13 mi (1,326.31 km) |
| Middle River to Oneida (New York) | 260.97 mi (420.00 km) |
| Middle River to Oneonta (New York) | 226.38 mi (364.33 km) |
| Middle River to Ontario (California) | 2,290.80 mi (3,686.68 km) |
| Middle River to Ontario (Oregon) | 2,095.74 mi (3,372.77 km) |
| Middle River to Opa-locka (Florida) | 954.98 mi (1,536.89 km) |
| Middle River to Opelika (Alabama) | 680.16 mi (1,094.62 km) |
| Middle River to Opelousas (Louisiana) | 1,073.43 mi (1,727.52 km) |
| Middle River to Orange (California) | 2,308.26 mi (3,714.79 km) |
| Middle River to Orange (Texas) | 1,169.31 mi (1,881.83 km) |
| Middle River to Orange City (Florida) | 770.73 mi (1,240.37 km) |
| Middle River to Orangeburg (South Carolina) | 473.56 mi (762.12 km) |
