| | San Luis Obispo, CA | Salem, NH | United States |
| Population | 47,257 | 30,158 | 329,725,481 |
| Female Population | 49.1% | 49.3% | 50.5% |
| Male Population | 50.9% | 50.7% | 49.5% |
| Median Age | 26 | 44.4 | 38.4 |
| space3 | | | |
| Population - 2010 | 45,193 | 28,760 | 309,327,143 |
| Population - 2000 | 44,174 | 28,112 | 285,036,114 |
| Population - 1990 | 41,958 | 25,746 | 251,960,433 |
| Pop. 2000 to Now | 7.7% | 9.0% | 15.6% |
| Pop. 1990 to Now | 13.4% | 19.0% | 30.8% |
| space4 | | | |
| Population Density | 3,597.8 | 1,219.7 | 93.4 |
| Land Area | 13.1 | 24.7 | 3,531,905.4 |
| Water Area | 0.2 | 1.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | San Luis Obispo, CA | Salem, NH | United States |
| Age 0 to 4 | 3.1% | 3.9% | 5.9% |
| Age 5 to 9 | 3.1% | 5.2% | 6.1% |
| Age 10 to 14 | 2.9% | 5.0% | 6.6% |
| Age 15 to 17 | 1.9% | 3.4% | 3.9% |
| Age 18 to 20 | 14.7% | 3.5% | 4.0% |
| Age 21 to 24 | 22.3% | 5.0% | 5.2% |
| Age 25 to 34 | 13.4% | 14.3% | 13.8% |
| Age 35 to 44 | 8.4% | 10.5% | 12.9% |
| Age 45 to 54 | 7.5% | 13.9% | 12.6% |
| Age 55 to 59 | 4.1% | 9.3% | 6.7% |
| Age 60 to 64 | 5.5% | 8.1% | 6.3% |
| Age 65 to 74 | 7.8% | 10.5% | 9.6% |
| Age 75 to 84 | 3.7% | 4.9% | 4.5% |
| Age 85 and over | 1.8% | 2.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | San Luis Obispo, CA | Salem, NH | United States |
| White | 70.7% | 83.4% | 59.4% |
| Black | 1.6% | 0.6% | 12.2% |
| Asian | 4.8% | 4.1% | 5.6% |
| Native American | 0.3% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.2% | 0.4% |
| Two or More Races | 3.9% | 3.0% | 3.2% |
| Hispanic | 18.5% | 8.7% | 18.4% |
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| Marriage & Family | | | |
| | San Luis Obispo, CA | Salem, NH | United States |
| Married Population | 28.8% | 56.4% | 49.8% |
| Currently Married | 27.9% | 54.7% | 48.0% |
| Married but Separated | 0.9% | 1.6% | 1.8% |
| Single Population | 71.2% | 43.6% | 50.2% |
| Never Married | 59.0% | 26.5% | 33.8% |
| Divorced | 8.3% | 11.3% | 10.8% |
| Widowed | 3.9% | 5.8% | 5.6% |
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| Household Size | 2.41 | 2.47 | 2.60 |
| Households | 19,035 | 12,138 | 124,010,992 |
| Family Households | 7,693 | 8,454 | 80,755,759 |
| Married couple, w/children | 23.1% | 27.4% | 30.5% |
| Married couple, no children | 49.4% | 52.3% | 42.9% |
| Non Family Households | 11,342 | 3,684 | 43,255,233 |
| Single householder, w/children | 12.1% | 11.3% | 15.8% |
| Single householder, no children | 15.3% | 9.0% | 10.8% |