| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 37°F | 25°F | 0.4" |
| February | 14°F | 36°F | 24°F | 0.6" |
| March | 23°F | 48°F | 34°F | 1.0" |
| April | 28°F | 53°F | 39°F | 2.4" |
| May | 37°F | 61°F | 48°F | 3.3" |
| June | 47°F | 74°F | 60°F | 2.9" |
| July | 53°F | 82°F | 67°F | 2.7" |
| August | 51°F | 80°F | 65°F | 2.4" |
| September | 43°F | 72°F | 56°F | 1.7" |
| October | 32°F | 57°F | 43°F | 1.3" |
| November | 23°F | 46°F | 34°F | 0.6" |
| December | 13°F | 35°F | 23°F | 0.7" |
| Index | Keystone | South Dakota | National |
| Air quality index | 44 | 36 | 42 |
| Pollution index | 1,968,790 | 345,623 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 274 |
| Days with moderate air quality | 87 |
| Days w/ poor A.Q. for sensitive groups | 4 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.020% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Hermosa, SD | 407 | 44 | 12.0% |
| Fairburn, SD | 104 | 44 | 12.0% |
| Hill City, SD | 587 | 44 | 12.0% |
| Colonial Pine Hills, SD | 2,720 | 44 | 12.0% |
| Johnson Siding, SD | 658 | 44 | 12.0% |
| Keystone, SD | 542 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Fonda, IA | 542 | 37 | 26.0% |
| Hayden, IN | 542 | 35 | 30.0% |
| Barlow, KY | 542 | 44 | 12.0% |
| Ethel, MS | 542 | 33 | 34.0% |
| Odessa, NY | 542 | 34 | 32.0% |
| Keystone, SD | 542 | 44 | 12.0% |
Here are the best places to live in South Dakota
Most Dangerous Cities In The US
See the best places to live in Keystone
These are the 10 cheapest cities in South Dakota