| | Cathcart, WA | Mill Creek, WA | United States |
| Population | 2,241 | 20,665 | 329,725,481 |
| Female Population | 48.0% | 53.1% | 50.5% |
| Male Population | 52.0% | 46.9% | 49.5% |
| Median Age | 47.3 | 39.6 | 38.4 |
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| Population - 2010 | 2,112 | 18,268 | 309,327,143 |
| Population - 2000 | 3,015 | 11,525 | 285,036,114 |
| Population - 1990 | 2,072 | 7,172 | 251,960,433 |
| Pop. 2000 to Now | -10.4% | 80.5% | 15.6% |
| Pop. 1990 to Now | 30.4% | 190.0% | 30.8% |
| space4 | | | |
| Population Density | 580.3 | 4,488.5 | 93.4 |
| Land Area | 3.9 | 4.6 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Cathcart, WA | Mill Creek, WA | United States |
| Age 0 to 4 | 6.9% | 5.5% | 5.9% |
| Age 5 to 9 | 0.8% | 5.9% | 6.1% |
| Age 10 to 14 | 4.2% | 6.8% | 6.6% |
| Age 15 to 17 | 3.4% | 3.3% | 3.9% |
| Age 18 to 20 | 5.4% | 2.4% | 4.0% |
| Age 21 to 24 | 0.8% | 4.8% | 5.2% |
| Age 25 to 34 | 21.6% | 14.7% | 13.8% |
| Age 35 to 44 | 3.9% | 13.8% | 12.9% |
| Age 45 to 54 | 11.7% | 13.9% | 12.6% |
| Age 55 to 59 | 10.2% | 7.3% | 6.7% |
| Age 60 to 64 | 15.5% | 5.9% | 6.3% |
| Age 65 to 74 | 10.2% | 8.7% | 9.6% |
| Age 75 to 84 | 3.8% | 4.9% | 4.5% |
| Age 85 and over | 1.5% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Cathcart, WA | Mill Creek, WA | United States |
| White | 96.1% | 60.2% | 59.4% |
| Black | 0.0% | 4.3% | 12.2% |
| Asian | 0.0% | 20.0% | 5.6% |
| Native American | 0.0% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.8% | 0.2% |
| Other | 0.0% | 0.5% | 0.4% |
| Two or More Races | 3.9% | 6.3% | 3.2% |
| Hispanic | 0.0% | 7.6% | 18.4% |
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| Marriage & Family | | | |
| | Cathcart, WA | Mill Creek, WA | United States |
| Married Population | 63.4% | 58.6% | 49.8% |
| Currently Married | 61.7% | 57.5% | 48.0% |
| Married but Separated | 1.7% | 1.2% | 1.8% |
| Single Population | 36.6% | 41.4% | 50.2% |
| Never Married | 27.0% | 26.9% | 33.8% |
| Divorced | 5.5% | 10.2% | 10.8% |
| Widowed | 4.1% | 4.2% | 5.6% |
| space5 | | | |
| Household Size | 2.76 | 2.42 | 2.60 |
| Households | 810 | 8,492 | 124,010,992 |
| Family Households | 605 | 5,410 | 80,755,759 |
| Married couple, w/children | 32.2% | 40.8% | 30.5% |
| Married couple, no children | 56.0% | 44.8% | 42.9% |
| Non Family Households | 205 | 3,082 | 43,255,233 |
| Single householder, w/children | 4.6% | 7.4% | 15.8% |
| Single householder, no children | 7.1% | 7.0% | 10.8% |