22 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Norwich | 1 | 39,986 | 40,018 | -0.02% | 1,425 | 28 | City |
| Groton | 2 | 39,668 | 38,329 | 2.34% | 1,275 | 31 | Township |
| New London | 3 | 28,404 | 26,789 | 1.15% | 5,066 | 6 | City |
| Windham | 4 | 24,137 | 23,859 | 0.13% | 899 | 27 | Township |
| Waterford | 5 | 19,986 | 19,570 | 0.38% | 608 | 33 | Township |
| Stonington | 6 | 19,105 | 18,319 | 1.72% | 494 | 39 | Township |
| East Lyme | 7 | 19,059 | 18,443 | 0.29% | 560 | 34 | Township |
| Montville | 8 | 18,024 | 18,061 | 0.62% | 431 | 42 | Township |
| Colchester | 9 | 15,807 | 15,495 | 0.35% | 323 | 49 | Township |
| Ledyard | 10 | 15,682 | 15,393 | 0.69% | 410 | 38 | Township |
| Griswold | 11 | 11,731 | 11,422 | 0.41% | 338 | 35 | Township |
| Lebanon | 12 | 7,169 | 7,129 | 0.39% | 133 | 54 | Township |
| North Stonington | 13 | 5,225 | 5,140 | 0.54% | 96 | 54 | Township |
| Colchester | 14 | 4,890 | 5,147 | 0.16% | 1,094 | 4 | CDP |
| Preston | 15 | 4,880 | 4,786 | 0.51% | 158 | 31 | Township |
| Salem | 16 | 4,336 | 4,198 | 0.23% | 150 | 29 | Township |
| Lisbon | 17 | 4,266 | 4,190 | 0.4% | 262 | 16 | Township |
| Waterford | 18 | 3,373 | 2,922 | 0.96% | 1,787 | 2 | CDP |
| Sprague | 19 | 2,958 | 2,960 | 0.34% | 223 | 13 | Township |
| Bozrah | 20 | 2,437 | 2,421 | 0.45% | 122 | 20 | Township |
| Franklin | 21 | 1,908 | 1,857 | 0.42% | 97 | 20 | Township |
| Stonington | 22 | 1,017 | 989 | 0.49% | 2,982 | 0 | Borough |
Norwich is the largest city in Southeastern CT Planning Region, with a population of 39,986.
Stonington is the smallest city in Southeastern CT Planning Region, with a population of 1,017.
There are 22 cities in Southeastern CT Planning Region, Connecticut.