12 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Odenton | Anne Arundel County | 47,536 |
| Owings Mills | Baltimore County | 36,781 |
| Olney | Montgomery County | 36,498 |
| Oxon Hill | Prince George's County | 18,668 |
| Overlea | Baltimore County | 12,466 |
| Ocean Pines | Worcester County | 12,101 |
| Ocean City | Worcester County | 6,901 |
| Owings | Calvert County | 2,550 |
| Oakland | Garrett County | 1,797 |
| Oxford | Talbot County | 597 |
| Oldtown | Allegany County | 92 |
| Ocean | Allegany County | 12 |