| | Spencer, MA | Lake St. Louis, MO | United States |
| Population | 11,963 | 16,665 | 329,725,481 |
| Female Population | 46.6% | 49.2% | 50.5% |
| Male Population | 53.4% | 50.8% | 49.5% |
| Median Age | 47.9 | 43.9 | 38.4 |
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| Population - 2010 | 11,715 | 14,607 | 309,327,143 |
| Population - 2000 | 11,691 | 10,169 | 285,036,114 |
| Population - 1990 | 11,645 | 8,355 | 251,960,433 |
| Pop. 2000 to Now | 1.8% | 69.0% | 15.6% |
| Pop. 1990 to Now | 2.2% | 105.7% | 30.8% |
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| Population Density | 364.4 | 2,002.5 | 93.4 |
| Land Area | 32.8 | 8.3 | 3,531,905.4 |
| Water Area | 1.2 | 0.8 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Spencer, MA | Lake St. Louis, MO | United States |
| Age 0 to 4 | 3.7% | 3.4% | 5.9% |
| Age 5 to 9 | 5.6% | 7.4% | 6.1% |
| Age 10 to 14 | 5.9% | 5.0% | 6.6% |
| Age 15 to 17 | 2.4% | 4.6% | 3.9% |
| Age 18 to 20 | 3.5% | 2.6% | 4.0% |
| Age 21 to 24 | 2.8% | 6.9% | 5.2% |
| Age 25 to 34 | 7.4% | 8.6% | 13.8% |
| Age 35 to 44 | 14.1% | 12.9% | 12.9% |
| Age 45 to 54 | 11.8% | 13.3% | 12.6% |
| Age 55 to 59 | 7.2% | 6.9% | 6.7% |
| Age 60 to 64 | 11.9% | 8.2% | 6.3% |
| Age 65 to 74 | 15.5% | 10.7% | 9.6% |
| Age 75 to 84 | 6.1% | 7.1% | 4.5% |
| Age 85 and over | 2.2% | 2.3% | 1.9% |
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| Race | | | |
| | Spencer, MA | Lake St. Louis, MO | United States |
| White | 91.1% | 86.6% | 59.4% |
| Black | 1.4% | 4.2% | 12.2% |
| Asian | 0.7% | 1.3% | 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 | 3.3% | 3.5% | 3.2% |
| Hispanic | 3.5% | 4.4% | 18.4% |
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| Marriage & Family | | | |
| | Spencer, MA | Lake St. Louis, MO | United States |
| Married Population | 55.2% | 63.1% | 49.8% |
| Currently Married | 54.8% | 62.8% | 48.0% |
| Married but Separated | 0.4% | 0.3% | 1.8% |
| Single Population | 44.8% | 36.9% | 50.2% |
| Never Married | 27.1% | 22.6% | 33.8% |
| Divorced | 13.8% | 10.3% | 10.8% |
| Widowed | 4.0% | 4.0% | 5.6% |
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| Household Size | 2.29 | 2.47 | 2.60 |
| Households | 5,186 | 6,747 | 124,010,992 |
| Family Households | 3,288 | 4,878 | 80,755,759 |
| Married couple, w/children | 25.3% | 34.6% | 30.5% |
| Married couple, no children | 55.7% | 55.5% | 42.9% |
| Non Family Households | 1,898 | 1,869 | 43,255,233 |
| Single householder, w/children | 12.2% | 6.9% | 15.8% |
| Single householder, no children | 6.8% | 3.0% | 10.8% |