| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 39°F | 29°F | 2.7" |
| February | 20°F | 40°F | 30°F | 2.9" |
| March | 28°F | 49°F | 38°F | 3.1" |
| April | 39°F | 63°F | 50°F | 3.6" |
| May | 48°F | 73°F | 60°F | 3.5" |
| June | 57°F | 80°F | 68°F | 5.1" |
| July | 64°F | 86°F | 74°F | 4.1" |
| August | 61°F | 83°F | 72°F | 4.2" |
| September | 54°F | 78°F | 65°F | 3.2" |
| October | 43°F | 66°F | 54°F | 4.1" |
| November | 33°F | 55°F | 43°F | 3.2" |
| December | 26°F | 44°F | 35°F | 4.0" |
| Index | Terryville | Connecticut | National |
| Air quality index | 37 | 43 | 42 |
| Pollution index | 14,500,300 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 342 |
| Days with moderate air quality | 23 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.080% |
| Mercury | 0.060% |
| City | Population | Air Quality Index | National Avg. |
| Bristol, CT | 60,039 | 37 | 26.0% |
| Oakville, CT | 9,679 | 37 | 26.0% |
| Litchfield, CT | 1,279 | 37 | 26.0% |
| Thomaston, CT | 1,730 | 37 | 26.0% |
| Northwest Harwinton, CT | 2,897 | 37 | 26.0% |
| Terryville, CT | 5,019 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Wapato, WA | 5,018 | 38 | 24.0% |
| Annapolis, Subd. C, NS | 5,018 | n/a | |
| Bret Harte, CA | 5,020 | 49 | 2.0% |
| White Hall, AR | 5,017 | 45 | 10.0% |
| South Haven, IN | 5,017 | 37 | 26.0% |
| Terryville, CT | 5,019 | 37 | 26.0% |
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