| | Clayton, CA | Missoula, MT | United States |
| Population | 11,136 | 73,300 | 329,725,481 |
| Female Population | 51.4% | 50.6% | 50.5% |
| Male Population | 48.6% | 49.4% | 49.5% |
| Median Age | 44.1 | 33.6 | 38.4 |
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| Population - 2010 | 10,941 | 67,497 | 309,327,143 |
| Population - 2000 | 10,762 | 57,053 | 285,036,114 |
| Population - 1990 | 7,317 | 42,918 | 251,960,433 |
| Pop. 2000 to Now | 7.1% | 34.7% | 15.6% |
| Pop. 1990 to Now | 57.5% | 79.1% | 30.8% |
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| Population Density | 2,900.0 | 2,504.7 | 93.4 |
| Land Area | 3.8 | 29.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Clayton, CA | Missoula, MT | United States |
| Age 0 to 4 | 3.8% | 4.7% | 5.9% |
| Age 5 to 9 | 5.6% | 4.2% | 6.1% |
| Age 10 to 14 | 9.0% | 5.8% | 6.6% |
| Age 15 to 17 | 5.8% | 2.8% | 3.9% |
| Age 18 to 20 | 3.3% | 6.1% | 4.0% |
| Age 21 to 24 | 6.3% | 10.9% | 5.2% |
| Age 25 to 34 | 6.8% | 18.0% | 13.8% |
| Age 35 to 44 | 11.0% | 14.0% | 12.9% |
| Age 45 to 54 | 13.2% | 10.1% | 12.6% |
| Age 55 to 59 | 10.0% | 5.2% | 6.7% |
| Age 60 to 64 | 7.8% | 4.8% | 6.3% |
| Age 65 to 74 | 9.7% | 8.9% | 9.6% |
| Age 75 to 84 | 6.4% | 3.2% | 4.5% |
| Age 85 and over | 1.5% | 1.5% | 1.9% |
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| Race | | | |
| | Clayton, CA | Missoula, MT | United States |
| White | 69.0% | 86.7% | 59.4% |
| Black | 1.5% | 0.6% | 12.2% |
| Asian | 11.4% | 1.7% | 5.6% |
| Native American | 0.1% | 1.9% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 0.4% | 0.4% | 0.4% |
| Two or More Races | 7.3% | 4.4% | 3.2% |
| Hispanic | 10.3% | 4.2% | 18.4% |
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| Marriage & Family | | | |
| | Clayton, CA | Missoula, MT | United States |
| Married Population | 56.9% | 39.2% | 49.8% |
| Currently Married | 55.5% | 38.1% | 48.0% |
| Married but Separated | 1.5% | 1.1% | 1.8% |
| Single Population | 43.1% | 60.8% | 50.2% |
| Never Married | 27.3% | 44.3% | 33.8% |
| Divorced | 8.8% | 12.8% | 10.8% |
| Widowed | 6.9% | 3.7% | 5.6% |
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| Household Size | 2.79 | 2.19 | 2.60 |
| Households | 3,986 | 32,233 | 124,010,992 |
| Family Households | 3,091 | 15,144 | 80,755,759 |
| Married couple, w/children | 35.1% | 31.9% | 30.5% |
| Married couple, no children | 45.3% | 43.3% | 42.9% |
| Non Family Households | 895 | 17,089 | 43,255,233 |
| Single householder, w/children | 10.2% | 15.3% | 15.8% |
| Single householder, no children | 9.4% | 9.5% | 10.8% |