10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Morgan City | 1 | 10,517 | 11,406 | -1.66% | 1,758 | 6 | City |
| Franklin | 2 | 6,118 | 6,675 | -1.78% | 614 | 10 | City |
| Patterson | 3 | 5,459 | 5,901 | -1.59% | 2,163 | 3 | City |
| Berwick | 4 | 4,390 | 4,742 | -1.57% | 744 | 6 | Town |
| Bayou Vista | 5 | 3,778 | 4,346 | -1.51% | 2,097 | 2 | CDP |
| Amelia | 6 | 1,885 | 2,236 | -2.03% | 748 | 3 | CDP |
| Baldwin | 7 | 1,632 | 1,749 | -1.39% | 507 | 3 | Town |
| Charenton | 8 | 838 | 1,560 | -7.81% | 169 | 5 | CDP |
| Centerville | 9 | 776 | 331 | 7.18% | 824 | 1 | CDP |
| Glencoe | 10 | 196 | 258 | -0.51% | 296 | 1 | CDP |
Morgan City is the largest city in St. Mary Parish, with a population of 10,517.
Glencoe is the smallest city in St. Mary Parish, with a population of 196.
There are 10 cities in St. Mary Parish, Louisiana.