18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Killingly | 1 | 18,229 | 17,716 | 0.75% | 377 | 48 | Township |
| Plainfield | 2 | 15,414 | 14,974 | 0.65% | 363 | 42 | Township |
| Thompson | 3 | 9,628 | 9,192 | 1.21% | 205 | 47 | Township |
| Putnam | 4 | 9,484 | 9,218 | 0.82% | 467 | 20 | Township |
| Brooklyn | 5 | 8,785 | 8,382 | 0.88% | 302 | 29 | Township |
| Woodstock | 6 | 8,512 | 8,224 | 0.92% | 140 | 61 | Township |
| Putnam | 7 | 7,205 | 7,138 | -0.01% | 1,848 | 4 | CDP |
| Canterbury | 8 | 5,295 | 5,048 | 1.4% | 133 | 40 | Township |
| Pomfret | 9 | 4,388 | 4,266 | 0.76% | 109 | 40 | Township |
| Ashford | 10 | 4,289 | 4,190 | 0.61% | 111 | 39 | Township |
| Sterling | 11 | 3,740 | 3,573 | 1.25% | 137 | 27 | Township |
| Voluntown | 12 | 2,682 | 2,568 | 1.21% | 69 | 39 | Township |
| Chaplin | 13 | 2,195 | 2,150 | 0.73% | 113 | 19 | Township |
| Hampton | 14 | 1,777 | 1,729 | 1.02% | 71 | 25 | Township |
| Eastford | 15 | 1,723 | 1,647 | 1% | 60 | 29 | Township |
| Scotland | 16 | 1,615 | 1,572 | 1.06% | 87 | 19 | Township |
| Brooklyn | 17 | 862 | 1,128 | -0.92% | 747 | 1 | CDP |
| Union | 18 | 812 | 782 | 0.87% | 28 | 29 | Township |
Killingly is the largest city in Northeastern CT Planning Region, with a population of 18,229.
Union is the smallest city in Northeastern CT Planning Region, with a population of 812.
There are 18 cities in Northeastern CT Planning Region, Connecticut.