12 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Odenton | Anne Arundel County | 47,000 |
| Owings Mills | Baltimore County | 36,093 |
| Olney | Montgomery County | 35,942 |
| Oxon Hill | Prince George's County | 18,727 |
| Overlea | Baltimore County | 12,924 |
| Ocean Pines | Worcester County | 12,462 |
| Ocean City | Worcester County | 6,961 |
| Owings | Calvert County | 2,433 |
| Oakland | Garrett County | 1,800 |
| Oxford | Talbot County | 594 |
| Oldtown | Allegany County | 109 |
| Ocean | Allegany County | 21 |