20 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Slidell | 1 | 28,392 | 28,688 | -0.17% | 1,859 | 15 | City |
| Slidell | 2 | 28,392 | 28,629 | -0.17% | 1,859 | 15 | City |
| Mandeville | 3 | 13,009 | 12,832 | 0.28% | 1,390 | 9 | City |
| Mandeville | 4 | 13,009 | 12,826 | 0.28% | 1,390 | 9 | City |
| Covington | 5 | 11,715 | 11,579 | 0.25% | 1,461 | 8 | City |
| Covington | 6 | 11,715 | 11,569 | 0.25% | 1,461 | 8 | City |
| Eden Isle | 7 | 8,975 | 8,103 | 1.46% | 2,955 | 3 | CDP |
| Lacombe | 8 | 6,624 | 7,294 | -2.03% | 250 | 26 | CDP |
| Abita Springs | 9 | 2,783 | 2,622 | 1.13% | 607 | 5 | Town |
| Abita Springs | 10 | 2,783 | 2,628 | 1.13% | 607 | 5 | Town |
| Pearl River | 11 | 2,673 | 2,533 | 0.98% | 716 | 4 | Town |
| Pearl River | 12 | 2,673 | 2,540 | 0.98% | 716 | 4 | Town |
| Madisonville | 13 | 882 | 847 | 0.8% | 349 | 3 | Town |
| Madisonville | 14 | 882 | 847 | 0.8% | 349 | 3 | Town |
| Folsom | 15 | 842 | 774 | 1.57% | 423 | 2 | Village |
| Folsom | 16 | 842 | 775 | 1.57% | 423 | 2 | Village |
| Lewisburg | 17 | 552 | 355 | 6.98% | 1,097 | 1 | CDP |
| Sun | 18 | 400 | 395 | 0.25% | 94 | 4 | Village |
| Sun | 19 | 400 | 394 | 0.25% | 94 | 4 | Village |
| Rio | 20 | 334 | 308 | 7.05% | 295 | 1 | CDP |
Slidell is the largest city in St. Tammany Parish, with a population of 28,392.
Rio is the smallest city in St. Tammany Parish, with a population of 334.
There are 20 cities in St. Tammany Parish, Louisiana.