12 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Slidell | 1 | 28,387 | 28,694 | -0.21% | 1,859 | 15.27 | City |
| Mandeville | 2 | 13,105 | 12,840 | 0.41% | 1,400 | 9.36 | City |
| Covington | 3 | 11,664 | 11,549 | 0.2% | 1,454 | 8.02 | City |
| Eden Isle | 4 | 8,975 | 8,103 | 1.46% | 2,955 | 3.04 | CDP |
| Lacombe | 5 | 6,624 | 7,294 | -2.03% | 250 | 26.45 | CDP |
| Abita Springs | 6 | 2,798 | 2,630 | 1.23% | 610 | 4.59 | Town |
| Pearl River | 7 | 2,704 | 2,563 | 1.05% | 724 | 3.73 | Town |
| Madisonville | 8 | 886 | 848 | 0.91% | 351 | 2.53 | Town |
| Folsom | 9 | 838 | 775 | 1.58% | 421 | 1.99 | Village |
| Lewisburg | 10 | 552 | 355 | 6.98% | 1,097 | 0.50 | CDP |
| Sun | 11 | 406 | 395 | 0.5% | 95 | 4.27 | Village |
| Rio | 12 | 334 | 308 | 7.05% | 295 | 1.13 | CDP |
Slidell is the largest city in St. Tammany Parish, with a population of 28,387.
Rio is the smallest city in St. Tammany Parish.
There are 12 cities in St. Tammany Parish, Louisiana.