20 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Groton | 1 | 40,574 | 38,329 | 2.28% | 1,304 | 31 | Township |
| Norwich | 2 | 39,980 | 40,018 | -0.02% | 1,425 | 28 | City |
| New London | 3 | 28,727 | 26,789 | 1.14% | 5,123 | 6 | City |
| Windham | 4 | 24,169 | 23,859 | 0.13% | 900 | 27 | Township |
| Waterford | 5 | 20,062 | 19,570 | 0.38% | 610 | 33 | Township |
| Stonington | 6 | 19,428 | 18,319 | 1.69% | 503 | 39 | Township |
| East Lyme | 7 | 19,114 | 18,443 | 0.29% | 562 | 34 | Township |
| Montville | 8 | 18,135 | 18,061 | 0.62% | 434 | 42 | Township |
| Colchester | 9 | 15,862 | 15,495 | 0.35% | 324 | 49 | Township |
| Ledyard | 10 | 15,789 | 15,393 | 0.68% | 413 | 38 | Township |
| Griswold | 11 | 11,779 | 11,422 | 0.41% | 339 | 35 | Township |
| Lebanon | 12 | 7,197 | 7,129 | 0.39% | 133 | 54 | Township |
| North Stonington | 13 | 5,253 | 5,140 | 0.54% | 97 | 54 | Township |
| Preston | 14 | 4,905 | 4,786 | 0.51% | 159 | 31 | Township |
| Salem | 15 | 4,346 | 4,198 | 0.23% | 150 | 29 | Township |
| Lisbon | 16 | 4,283 | 4,190 | 0.4% | 263 | 16 | Township |
| Sprague | 17 | 2,968 | 2,960 | 0.34% | 224 | 13 | Township |
| Bozrah | 18 | 2,448 | 2,421 | 0.45% | 123 | 20 | Township |
| Franklin | 19 | 1,916 | 1,857 | 0.42% | 97 | 20 | Township |
| Stonington | 20 | 1,023 | 989 | 0.59% | 3,000 | 0 | Borough |
Groton is the largest city in Southeastern CT Planning Region, with a population of 40,574.
Stonington is the smallest city in Southeastern CT Planning Region, with a population of 1,023.
There are 20 cities in Southeastern CT Planning Region, Connecticut.