| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Morgan City | 1 | 10,620 | 11,412 | -1.27% | 1,775 | 6 | City |
| Franklin | 2 | 6,134 | 6,658 | -1.45% | 616 | 10 | City |
| Patterson | 3 | 5,495 | 5,904 | -1.26% | 2,177 | 3 | City |
| Berwick | 4 | 4,393 | 4,742 | -1.39% | 744 | 6 | Town |
| Baldwin | 5 | 1,660 | 1,747 | -0.95% | 516 | 3 | Town |
Morgan City is the largest city in St. Mary Parish, with a population of 10,620.
Baldwin is the smallest city in St. Mary Parish, with a population of 1,660.
There are 5 cities in St. Mary Parish, Louisiana.