| | Williamstown, KY | Petersburg, KY | United States |
| Population | 3,926 | 418 | 329,725,481 |
| Female Population | 54.1% | 54.1% | 50.5% |
| Male Population | 46.0% | 45.9% | 49.5% |
| Median Age | 31.2 | 33.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,917 | 723 | 309,327,143 |
| Population - 2000 | 3,227 | 664 | 285,036,114 |
| Population - 1990 | 3,023 | 592 | 251,960,433 |
| Pop. 2000 to Now | 22.1% | -6.2% | 15.6% |
| Pop. 1990 to Now | 30.3% | 5.2% | 30.8% |
| space4 | | | |
| Population Density | 235.0 | 66.6 | 93.4 |
| Land Area | 16.7 | 6.3 | 3,531,905.4 |
| Water Area | 0.5 | 0.7 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Williamstown, KY | Petersburg, KY | United States |
| Age 0 to 4 | 12.6% | 9.1% | 5.9% |
| Age 5 to 9 | 6.2% | 3.6% | 6.1% |
| Age 10 to 14 | 6.9% | 10.8% | 6.6% |
| Age 15 to 17 | 4.8% | 6.9% | 3.9% |
| Age 18 to 20 | 1.8% | 3.1% | 4.0% |
| Age 21 to 24 | 5.8% | 8.4% | 5.2% |
| Age 25 to 34 | 18.6% | 20.6% | 13.8% |
| Age 35 to 44 | 12.4% | 2.2% | 12.9% |
| Age 45 to 54 | 10.6% | 10.3% | 12.6% |
| Age 55 to 59 | 3.1% | 2.2% | 6.7% |
| Age 60 to 64 | 4.3% | 0.0% | 6.3% |
| Age 65 to 74 | 5.8% | 23.0% | 9.6% |
| Age 75 to 84 | 3.7% | 0.0% | 4.5% |
| Age 85 and over | 3.4% | 0.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Williamstown, KY | Petersburg, KY | United States |
| White | 88.1% | 98.1% | 59.4% |
| Black | 0.6% | 0.0% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.0% | 0.4% |
| Two or More Races | 11.2% | 1.9% | 3.2% |
| Hispanic | 0.0% | 0.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Williamstown, KY | Petersburg, KY | United States |
| Married Population | 52.7% | 35.0% | 49.8% |
| Currently Married | 47.3% | 35.0% | 48.0% |
| Married but Separated | 5.3% | 0.0% | 1.8% |
| Single Population | 47.3% | 65.0% | 50.2% |
| Never Married | 26.0% | 49.4% | 33.8% |
| Divorced | 14.4% | 12.8% | 10.8% |
| Widowed | 6.9% | 2.8% | 5.6% |
| space5 | | | |
| Household Size | 2.63 | 3.37 | 2.60 |
| Households | 1,370 | 124 | 124,010,992 |
| Family Households | 922 | 124 | 80,755,759 |
| Married couple, w/children | 41.6% | 14.5% | 30.5% |
| Married couple, no children | 31.0% | 34.7% | 42.9% |
| Non Family Households | 448 | 0 | 43,255,233 |
| Single householder, w/children | 25.7% | 21.8% | 15.8% |
| Single householder, no children | 1.6% | 29.0% | 10.8% |