| | Southbridge Town, MA | Gardner, MA | United States |
| Population | 17,643 | 21,183 | 329,725,481 |
| Female Population | 52.1% | 47.0% | 50.5% |
| Male Population | 47.9% | 53.0% | 49.5% |
| Median Age | 40.6 | 44.3 | 38.4 |
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| Population - 2010 | 16,721 | 20,174 | 309,327,143 |
| Population - 2000 | 17,217 | 20,770 | 285,036,114 |
| Population - 1990 | 17,816 | 20,125 | 251,960,433 |
| Pop. 2000 to Now | -2.5% | -0.9% | 15.6% |
| Pop. 1990 to Now | -5.8% | 2.3% | 30.8% |
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| Population Density | 871.8 | 959.9 | 93.4 |
| Land Area | 20.2 | 22.1 | 3,531,905.4 |
| Water Area | 0.6 | 0.9 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Southbridge Town, MA | Gardner, MA | United States |
| Age 0 to 4 | 7.0% | 5.3% | 5.9% |
| Age 5 to 9 | 5.7% | 4.6% | 6.1% |
| Age 10 to 14 | 4.9% | 5.4% | 6.6% |
| Age 15 to 17 | 4.6% | 2.3% | 3.9% |
| Age 18 to 20 | 2.5% | 2.6% | 4.0% |
| Age 21 to 24 | 7.6% | 3.2% | 5.2% |
| Age 25 to 34 | 12.7% | 15.8% | 13.8% |
| Age 35 to 44 | 9.8% | 11.7% | 12.9% |
| Age 45 to 54 | 15.2% | 13.0% | 12.6% |
| Age 55 to 59 | 9.1% | 7.7% | 6.7% |
| Age 60 to 64 | 6.2% | 10.3% | 6.3% |
| Age 65 to 74 | 8.2% | 10.2% | 9.6% |
| Age 75 to 84 | 4.7% | 4.9% | 4.5% |
| Age 85 and over | 1.9% | 3.1% | 1.9% |
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| Race | | | |
| | Southbridge Town, MA | Gardner, MA | United States |
| White | 59.9% | 82.5% | 59.4% |
| Black | 3.0% | 2.0% | 12.2% |
| Asian | 0.8% | 3.1% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 2.1% | 2.9% | 3.2% |
| Hispanic | 34.1% | 9.1% | 18.4% |
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| Marriage & Family | | | |
| | Southbridge Town, MA | Gardner, MA | United States |
| Married Population | 38.7% | 46.6% | 49.8% |
| Currently Married | 36.2% | 44.7% | 48.0% |
| Married but Separated | 2.5% | 1.9% | 1.8% |
| Single Population | 61.3% | 53.4% | 50.2% |
| Never Married | 39.4% | 33.8% | 33.8% |
| Divorced | 15.2% | 12.4% | 10.8% |
| Widowed | 6.8% | 7.2% | 5.6% |
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| Household Size | 2.46 | 2.25 | 2.60 |
| Households | 7,094 | 8,841 | 124,010,992 |
| Family Households | 4,351 | 5,446 | 80,755,759 |
| Married couple, w/children | 20.9% | 21.3% | 30.5% |
| Married couple, no children | 34.1% | 48.6% | 42.9% |
| Non Family Households | 2,743 | 3,395 | 43,255,233 |
| Single householder, w/children | 29.9% | 19.8% | 15.8% |
| Single householder, no children | 15.1% | 10.3% | 10.8% |