5 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Morgan City | 1 | 10,663 | 11,411 | -1.39% | 1,782 | 6 | City |
| Franklin | 2 | 6,187 | 6,670 | -1.54% | 621 | 10 | City |
| Patterson | 3 | 5,540 | 5,907 | -1.32% | 2,195 | 3 | City |
| Berwick | 4 | 4,432 | 4,744 | -1.4% | 751 | 6 | Town |
| Baldwin | 5 | 1,644 | 1,747 | -1.26% | 511 | 3 | Town |
Morgan City is the largest city in St. Mary Parish, with a population of 10,663.
Baldwin is the smallest city in St. Mary Parish, with a population of 1,644.
There are 5 cities in St. Mary Parish, Louisiana.