| | Southgate, MI | Port Huron, MI | United States |
| Population | 29,990 | 29,009 | 329,725,481 |
| Female Population | 52.0% | 50.1% | 50.5% |
| Male Population | 48.1% | 49.9% | 49.5% |
| Median Age | 42.1 | 39 | 38.4 |
| space3 | | | |
| Population - 2010 | 29,977 | 30,110 | 309,327,143 |
| Population - 2000 | 30,136 | 32,338 | 285,036,114 |
| Population - 1990 | 30,771 | 33,694 | 251,960,433 |
| Pop. 2000 to Now | -3.3% | -11.5% | 15.6% |
| Pop. 1990 to Now | -5.3% | -15.0% | 30.8% |
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| Population Density | 4,362.2 | 3,580.5 | 93.4 |
| Land Area | 6.9 | 8.1 | 3,531,905.4 |
| Water Area | 0.0 | 4.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Southgate, MI | Port Huron, MI | United States |
| Age 0 to 4 | 5.5% | 5.8% | 5.9% |
| Age 5 to 9 | 5.2% | 6.1% | 6.1% |
| Age 10 to 14 | 5.6% | 6.4% | 6.6% |
| Age 15 to 17 | 2.5% | 4.0% | 3.9% |
| Age 18 to 20 | 2.2% | 3.8% | 4.0% |
| Age 21 to 24 | 5.5% | 5.5% | 5.2% |
| Age 25 to 34 | 16.2% | 14.3% | 13.8% |
| Age 35 to 44 | 11.4% | 12.0% | 12.9% |
| Age 45 to 54 | 12.8% | 12.2% | 12.6% |
| Age 55 to 59 | 6.9% | 6.9% | 6.7% |
| Age 60 to 64 | 8.0% | 6.5% | 6.3% |
| Age 65 to 74 | 10.9% | 10.0% | 9.6% |
| Age 75 to 84 | 4.9% | 3.3% | 4.5% |
| Age 85 and over | 2.4% | 3.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Southgate, MI | Port Huron, MI | United States |
| White | 78.7% | 77.2% | 59.4% |
| Black | 6.2% | 7.5% | 12.2% |
| Asian | 2.3% | 0.6% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.0% | 0.2% | 0.4% |
| Two or More Races | 2.4% | 6.2% | 3.2% |
| Hispanic | 10.4% | 8.1% | 18.4% |
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| Marriage & Family | | | |
| | Southgate, MI | Port Huron, MI | United States |
| Married Population | 45.1% | 40.7% | 49.8% |
| Currently Married | 43.9% | 38.8% | 48.0% |
| Married but Separated | 1.1% | 2.0% | 1.8% |
| Single Population | 54.9% | 59.3% | 50.2% |
| Never Married | 34.3% | 37.1% | 33.8% |
| Divorced | 13.2% | 16.5% | 10.8% |
| Widowed | 7.5% | 5.7% | 5.6% |
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| Household Size | 2.38 | 2.35 | 2.60 |
| Households | 12,566 | 12,179 | 124,010,992 |
| Family Households | 7,562 | 7,301 | 80,755,759 |
| Married couple, w/children | 24.3% | 18.7% | 30.5% |
| Married couple, no children | 44.4% | 39.4% | 42.9% |
| Non Family Households | 5,004 | 4,878 | 43,255,233 |
| Single householder, w/children | 18.1% | 27.4% | 15.8% |
| Single householder, no children | 13.2% | 14.5% | 10.8% |