| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Northeastern CT Planning Region | 1 | 2.69% | 97,780 | 95,222 |
| Naugatuck Valley Planning Region | 2 | 2.65% | 461,204 | 449,285 |
| Capitol Planning Region | 3 | 2.02% | 981,848 | 962,436 |
| Lower CT River Valley Planning Region | 4 | 1.97% | 176,681 | 173,268 |
| Northwest Hills Planning Region | 5 | 1.46% | 113,835 | 112,202 |
| Greater Bridgeport Planning Region | 6 | 1.33% | 328,703 | 324,387 |
| Western CT Planning Region | 7 | 1.24% | 626,007 | 618,368 |
| Southeastern CT Planning Region | 8 | 0.74% | 280,388 | 278,342 |
| South Central CT Planning Region | 9 | 0.64% | 567,670 | 564,076 |
Connecticut's counties show varied growth patterns from 2020 to 2025. Northeastern CT Planning Region leads with 2.69% annualized growth, followed by Naugatuck Valley Planning Region (2.65%) and Capitol Planning Region (2.02%). The largest counties are Capitol Planning Region (981,848), Western CT Planning Region (626,007), and South Central CT Planning Region (567,670). All 9 counties in Connecticut are growing. Overall, counties averaged 1.64% annualized growth, with total population growing by 1.58% annually.