21 cities
| City | 2026 Pop. ↓ |
|---|---|
| Osasco | 699,944 |
| Olinda | 393,115 |
| Ourinhos | 114,352 |
| Ouro Preto | 63,678 |
| Olimpia | 45,199 |
| Orlandia | 44,766 |
| Oriximina | 35,581 |
| Oliveira | 34,710 |
| Osorio | 34,628 |
| Ouricuri | 29,317 |
| Ouro Branco | 26,687 |
| Ouro Preto do Oeste | 26,683 |
| Osvaldo Cruz | 25,746 |
| Obidos | 24,970 |
| Oeiras | 21,071 |
| Orleans | 16,422 |
| Oros | 16,328 |
| Otacilio Costa | 14,557 |
| Olindina | 12,316 |
| Ortigueira | 11,540 |
| Oeiras do Para | 10,162 |