| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 61°F | 49°F | 4.4" |
| February | 37°F | 60°F | 48°F | 6.9" |
| March | 43°F | 70°F | 56°F | 7.0" |
| April | 49°F | 76°F | 62°F | 7.0" |
| May | 56°F | 83°F | 69°F | 4.0" |
| June | 68°F | 88°F | 77°F | 7.7" |
| July | 71°F | 91°F | 80°F | 10.1" |
| August | 73°F | 93°F | 82°F | 7.0" |
| September | 67°F | 89°F | 77°F | 3.3" |
| October | 58°F | 80°F | 68°F | 5.5" |
| November | 43°F | 71°F | 56°F | 3.5" |
| December | 40°F | 63°F | 50°F | 7.2" |
| Index | Harleyville | South Carolina | National |
| Air quality index | 29 | 37 | 42 |
| Pollution index | 783,589 | 3,620,438 | 2,726,193 |
| Measurement | Total |
| Days measured | 7 |
| Days with good air quality | 7 |
| Days with moderate air quality | 0 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.003% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Holly Hill, SC | 1,469 | 29 | 42.0% |
| St. George, SC | 2,209 | 29 | 42.0% |
| Ridgeville, SC | 1,849 | 29 | 42.0% |
| Bowman, SC | 617 | 29 | 42.0% |
| Eutawville, SC | 515 | 29 | 42.0% |
| Harleyville, SC | 658 | 29 | 42.0% |
| City | Population | Air Quality Index | National Avg. |
| Ona, FL | 658 | 36 | 28.0% |
| Melba, ID | 658 | 36 | 28.0% |
| Marengo, IN | 658 | 6 | 88.0% |
| Russell, MA | 658 | 40 | 20.0% |
| Marshall, NC | 658 | 44 | 12.0% |
| Harleyville, SC | 658 | 29 | 42.0% |
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