| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 33°F | 55°F | 43°F | 4.5" |
| February | 34°F | 56°F | 44°F | 3.6" |
| March | 41°F | 66°F | 53°F | 4.7" |
| April | 49°F | 74°F | 61°F | 3.4" |
| May | 58°F | 80°F | 69°F | 4.0" |
| June | 67°F | 89°F | 77°F | 4.0" |
| July | 70°F | 90°F | 79°F | 4.5" |
| August | 71°F | 91°F | 80°F | 3.4" |
| September | 64°F | 84°F | 73°F | 3.4" |
| October | 52°F | 73°F | 62°F | 4.1" |
| November | 41°F | 64°F | 52°F | 3.1" |
| December | 36°F | 56°F | 45°F | 6.2" |
| Index | Williamston | South Carolina | National |
| Air quality index | 31 | 37 | 42 |
| Pollution index | 1,548,730 | 3,620,438 | 2,726,193 |
| Measurement | Total |
| Days measured | 250 |
| Days with good air quality | 248 |
| Days with moderate air quality | 2 |
| Days w/ poor A.Q. for sensitive groups | |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.030% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Princeton, SC | 60 | 31 | 38.0% |
| Pelzer, SC | 1,653 | 31 | 38.0% |
| Homeland Park, SC | 6,570 | 31 | 38.0% |
| Anderson, SC | 27,387 | 31 | 38.0% |
| Honea Path, SC | 3,753 | 31 | 38.0% |
| Williamston, SC | 4,219 | 31 | 38.0% |
| City | Population | Air Quality Index | National Avg. |
| Simonds, NB | 4,219 | n/a | |
| Le Roy, NY | 4,220 | 37 | 26.0% |
| Apison, TN | 4,220 | 46 | 8.0% |
| Pittsboro, NC | 4,221 | 29 | 42.0% |
| Hometown, IL | 4,216 | 55 | 10.0% |
| Williamston, SC | 4,219 | 31 | 38.0% |
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