| | Johnston, SC | Pen Argyl, PA | United States |
| Population | 2,248 | 3,518 | 329,725,481 |
| Female Population | 54.2% | 50.5% | 50.5% |
| Male Population | 45.8% | 49.5% | 49.5% |
| Median Age | 46.7 | 35.3 | 38.4 |
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| Population - 2010 | 2,371 | 3,589 | 309,327,143 |
| Population - 2000 | 2,336 | 3,615 | 285,036,114 |
| Population - 1990 | 2,688 | 3,492 | 251,960,433 |
| Pop. 2000 to Now | 2.5% | -2.1% | 15.6% |
| Pop. 1990 to Now | -10.9% | 1.4% | 30.8% |
| space4 | | | |
| Population Density | 848.9 | 2,621.5 | 93.4 |
| Land Area | 2.6 | 1.3 | 3,531,905.4 |
| Water Area | 0.1 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Johnston, SC | Pen Argyl, PA | United States |
| Age 0 to 4 | 5.3% | 5.2% | 5.9% |
| Age 5 to 9 | 3.2% | 7.2% | 6.1% |
| Age 10 to 14 | 6.1% | 7.1% | 6.6% |
| Age 15 to 17 | 4.5% | 0.9% | 3.9% |
| Age 18 to 20 | 3.0% | 5.5% | 4.0% |
| Age 21 to 24 | 4.2% | 6.1% | 5.2% |
| Age 25 to 34 | 12.2% | 17.3% | 13.8% |
| Age 35 to 44 | 9.4% | 11.7% | 12.9% |
| Age 45 to 54 | 13.3% | 12.9% | 12.6% |
| Age 55 to 59 | 6.5% | 8.8% | 6.7% |
| Age 60 to 64 | 5.5% | 6.5% | 6.3% |
| Age 65 to 74 | 15.3% | 6.3% | 9.6% |
| Age 75 to 84 | 6.5% | 2.4% | 4.5% |
| Age 85 and over | 5.0% | 2.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Johnston, SC | Pen Argyl, PA | United States |
| White | 27.8% | 86.4% | 59.4% |
| Black | 67.9% | 2.9% | 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 | 0.0% | 0.0% | 0.4% |
| Two or More Races | 1.3% | 2.8% | 3.2% |
| Hispanic | 3.0% | 8.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Johnston, SC | Pen Argyl, PA | United States |
| Married Population | 43.8% | 58.2% | 49.8% |
| Currently Married | 37.0% | 53.3% | 48.0% |
| Married but Separated | 6.9% | 4.9% | 1.8% |
| Single Population | 56.2% | 41.8% | 50.2% |
| Never Married | 35.8% | 30.3% | 33.8% |
| Divorced | 11.0% | 8.9% | 10.8% |
| Widowed | 9.4% | 2.6% | 5.6% |
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| Household Size | 2.33 | 2.63 | 2.60 |
| Households | 963 | 1,327 | 124,010,992 |
| Family Households | 535 | 1,005 | 80,755,759 |
| Married couple, w/children | 5.4% | 22.6% | 30.5% |
| Married couple, no children | 37.2% | 53.1% | 42.9% |
| Non Family Households | 428 | 322 | 43,255,233 |
| Single householder, w/children | 40.0% | 18.5% | 15.8% |
| Single householder, no children | 17.4% | 5.8% | 10.8% |