| | McComb, MS | Johnson City, TN | United States |
| Population | 12,400 | 69,521 | 329,725,481 |
| Female Population | 57.0% | 52.0% | 50.5% |
| Male Population | 43.0% | 48.0% | 49.5% |
| Median Age | 37.2 | 35.3 | 38.4 |
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| Population - 2010 | 12,763 | 63,525 | 309,327,143 |
| Population - 2000 | 13,337 | 55,469 | 285,036,114 |
| Population - 1990 | 11,591 | 49,381 | 251,960,433 |
| Pop. 2000 to Now | -3.9% | 21.0% | 15.6% |
| Pop. 1990 to Now | 10.5% | 36.0% | 30.8% |
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| Population Density | 1,071.1 | 1,613.5 | 93.4 |
| Land Area | 11.6 | 43.1 | 3,531,905.4 |
| Water Area | 0.1 | 0.3 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | McComb, MS | Johnson City, TN | United States |
| Age 0 to 4 | 6.6% | 5.6% | 5.9% |
| Age 5 to 9 | 10.1% | 5.9% | 6.1% |
| Age 10 to 14 | 5.7% | 5.2% | 6.6% |
| Age 15 to 17 | 3.7% | 2.9% | 3.9% |
| Age 18 to 20 | 5.2% | 7.2% | 4.0% |
| Age 21 to 24 | 3.1% | 8.5% | 5.2% |
| Age 25 to 34 | 11.6% | 14.4% | 13.8% |
| Age 35 to 44 | 11.4% | 11.7% | 12.9% |
| Age 45 to 54 | 11.1% | 11.7% | 12.6% |
| Age 55 to 59 | 6.0% | 5.7% | 6.7% |
| Age 60 to 64 | 7.2% | 6.4% | 6.3% |
| Age 65 to 74 | 10.4% | 8.9% | 9.6% |
| Age 75 to 84 | 5.7% | 4.1% | 4.5% |
| Age 85 and over | 2.2% | 1.9% | 1.9% |
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| Race | | | |
| | McComb, MS | Johnson City, TN | United States |
| White | 22.7% | 81.7% | 59.4% |
| Black | 75.0% | 6.8% | 12.2% |
| Asian | 0.4% | 2.6% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 0.1% | 3.2% | 3.2% |
| Hispanic | 1.7% | 5.5% | 18.4% |
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| Marriage & Family | | | |
| | McComb, MS | Johnson City, TN | United States |
| Married Population | 34.5% | 43.0% | 49.8% |
| Currently Married | 30.4% | 41.2% | 48.0% |
| Married but Separated | 4.1% | 1.9% | 1.8% |
| Single Population | 65.5% | 57.0% | 50.2% |
| Never Married | 39.6% | 38.0% | 33.8% |
| Divorced | 16.3% | 12.0% | 10.8% |
| Widowed | 9.5% | 7.0% | 5.6% |
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| Household Size | 2.26 | 2.23 | 2.60 |
| Households | 5,340 | 29,425 | 124,010,992 |
| Family Households | 2,314 | 15,929 | 80,755,759 |
| Married couple, w/children | 16.6% | 26.4% | 30.5% |
| Married couple, no children | 36.5% | 44.9% | 42.9% |
| Non Family Households | 3,026 | 13,496 | 43,255,233 |
| Single householder, w/children | 26.6% | 19.5% | 15.8% |
| Single householder, no children | 20.3% | 9.2% | 10.8% |