| | St. Marys, KS | St. Maries, ID | United States |
| Population | 2,782 | 2,951 | 329,725,481 |
| Female Population | 50.5% | 50.9% | 50.5% |
| Male Population | 49.5% | 49.1% | 49.5% |
| Median Age | 27.1 | 39.3 | 38.4 |
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| Population - 2010 | 2,680 | 2,500 | 309,327,143 |
| Population - 2000 | 2,198 | 2,652 | 285,036,114 |
| Population - 1990 | 1,791 | 2,442 | 251,960,433 |
| Pop. 2000 to Now | 20.7% | -7.1% | 15.6% |
| Pop. 1990 to Now | 48.1% | 0.9% | 30.8% |
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| Population Density | 2,349.7 | 2,486.1 | 93.4 |
| Land Area | 1.2 | 1.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Marys, KS | St. Maries, ID | United States |
| Age 0 to 4 | 9.3% | 8.6% | 5.9% |
| Age 5 to 9 | 7.8% | 5.3% | 6.1% |
| Age 10 to 14 | 8.2% | 6.9% | 6.6% |
| Age 15 to 17 | 5.2% | 3.6% | 3.9% |
| Age 18 to 20 | 6.8% | 1.6% | 4.0% |
| Age 21 to 24 | 7.0% | 7.5% | 5.2% |
| Age 25 to 34 | 17.4% | 10.5% | 13.8% |
| Age 35 to 44 | 7.1% | 11.5% | 12.9% |
| Age 45 to 54 | 6.7% | 12.6% | 12.6% |
| Age 55 to 59 | 8.2% | 9.3% | 6.7% |
| Age 60 to 64 | 2.6% | 6.6% | 6.3% |
| Age 65 to 74 | 9.0% | 6.6% | 9.6% |
| Age 75 to 84 | 3.4% | 6.1% | 4.5% |
| Age 85 and over | 1.5% | 3.2% | 1.9% |
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| Race | | | |
| | St. Marys, KS | St. Maries, ID | United States |
| White | 83.2% | 94.3% | 59.4% |
| Black | 0.8% | 0.0% | 12.2% |
| Asian | 4.6% | 0.3% | 5.6% |
| Native American | 0.1% | 0.5% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 2.5% | 0.0% | 0.4% |
| Two or More Races | 3.6% | 2.1% | 3.2% |
| Hispanic | 5.2% | 2.6% | 18.4% |
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| Marriage & Family | | | |
| | St. Marys, KS | St. Maries, ID | United States |
| Married Population | 55.7% | 48.2% | 49.8% |
| Currently Married | 55.4% | 46.4% | 48.0% |
| Married but Separated | 0.3% | 1.8% | 1.8% |
| Single Population | 44.3% | 51.8% | 50.2% |
| Never Married | 33.9% | 24.1% | 33.8% |
| Divorced | 6.2% | 20.7% | 10.8% |
| Widowed | 4.2% | 7.0% | 5.6% |
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| Household Size | 3.18 | 2.54 | 2.60 |
| Households | 866 | 1,135 | 124,010,992 |
| Family Households | 650 | 668 | 80,755,759 |
| Married couple, w/children | 46.3% | 41.0% | 30.5% |
| Married couple, no children | 41.8% | 34.3% | 42.9% |
| Non Family Households | 216 | 467 | 43,255,233 |
| Single householder, w/children | 5.8% | 14.2% | 15.8% |
| Single householder, no children | 6.0% | 10.5% | 10.8% |