| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 34°F | 25°F | 3.1" |
| February | 18°F | 36°F | 27°F | 2.2" |
| March | 28°F | 50°F | 38°F | 2.7" |
| April | 38°F | 64°F | 50°F | 3.6" |
| May | 48°F | 74°F | 61°F | 4.2" |
| June | 58°F | 83°F | 70°F | 4.2" |
| July | 62°F | 85°F | 73°F | 4.5" |
| August | 60°F | 83°F | 72°F | 4.9" |
| September | 53°F | 78°F | 65°F | 4.0" |
| October | 43°F | 65°F | 53°F | 4.5" |
| November | 32°F | 52°F | 41°F | 2.6" |
| December | 22°F | 38°F | 30°F | 2.8" |
| Index | Plymouth | Indiana | National |
| Air quality index | 42 | 56 | 42 |
| Pollution index | 4,961,970 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 275 |
| Days with moderate air quality | 90 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.060% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.020% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Mentone, IN | 1,199 | 37 | 26.0% |
| Etna Green, IN | 565 | 37 | 26.0% |
| North Liberty, IN | 1,822 | 42 | 16.0% |
| Bourbon, IN | 1,942 | 42 | 16.0% |
| Lakeville, IN | 765 | 42 | 16.0% |
| Plymouth, IN | 10,029 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Brandon, SD | 10,030 | 36 | 28.0% |
| Westgate, FL | 10,027 | 36 | 28.0% |
| Berlin, NH | 10,025 | 40 | 20.0% |
| The Pinery, CO | 10,033 | 58 | 16.0% |
| Elkhorn, WI | 10,034 | 37 | 26.0% |
| Plymouth, IN | 10,029 | 42 | 16.0% |
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