| | Waltham, MA | Louisville, KY | United States |
| Population | 64,655 | 630,260 | 329,725,481 |
| Female Population | 50.8% | 51.4% | 50.5% |
| Male Population | 49.2% | 48.6% | 49.5% |
| Median Age | 33.8 | 37.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 60,912 | 596,518 | 309,327,143 |
| Population - 2000 | 59,226 | 584,729 | 285,036,114 |
| Population - 1990 | 57,878 | 564,366 | 251,960,433 |
| Pop. 2000 to Now | 4.8% | 5.8% | 15.6% |
| Pop. 1990 to Now | 7.2% | 9.6% | 30.8% |
| space4 | | | |
| Population Density | 5,075.8 | 2,392.8 | 93.4 |
| Land Area | 12.7 | 263.4 | 3,531,905.4 |
| Water Area | 1.0 | 11.8 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Waltham, MA | Louisville, KY | United States |
| Age 0 to 4 | 5.0% | 6.2% | 5.9% |
| Age 5 to 9 | 3.5% | 6.0% | 6.1% |
| Age 10 to 14 | 3.5% | 6.4% | 6.6% |
| Age 15 to 17 | 2.0% | 3.8% | 3.9% |
| Age 18 to 20 | 9.4% | 3.9% | 4.0% |
| Age 21 to 24 | 10.9% | 5.2% | 5.2% |
| Age 25 to 34 | 18.1% | 14.8% | 13.8% |
| Age 35 to 44 | 12.2% | 12.8% | 12.9% |
| Age 45 to 54 | 9.9% | 12.3% | 12.6% |
| Age 55 to 59 | 6.4% | 6.7% | 6.7% |
| Age 60 to 64 | 4.7% | 6.7% | 6.3% |
| Age 65 to 74 | 8.5% | 9.3% | 9.6% |
| Age 75 to 84 | 4.4% | 4.2% | 4.5% |
| Age 85 and over | 1.7% | 1.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Waltham, MA | Louisville, KY | United States |
| White | 63.8% | 63.8% | 59.4% |
| Black | 6.5% | 23.5% | 12.2% |
| Asian | 12.1% | 2.7% | 5.6% |
| Native American | 0.2% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.1% | 0.2% |
| Other | 0.3% | 0.4% | 0.4% |
| Two or More Races | 2.6% | 3.0% | 3.2% |
| Hispanic | 14.5% | 6.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Waltham, MA | Louisville, KY | United States |
| Married Population | 38.2% | 44.1% | 49.8% |
| Currently Married | 36.9% | 42.0% | 48.0% |
| Married but Separated | 1.3% | 2.1% | 1.8% |
| Single Population | 61.8% | 55.9% | 50.2% |
| Never Married | 49.3% | 36.9% | 33.8% |
| Divorced | 7.3% | 12.7% | 10.8% |
| Widowed | 5.1% | 6.3% | 5.6% |
| space5 | | | |
| Household Size | 2.27 | 2.39 | 2.60 |
| Households | 24,943 | 257,758 | 124,010,992 |
| Family Households | 12,675 | 151,846 | 80,755,759 |
| Married couple, w/children | 29.5% | 26.2% | 30.5% |
| Married couple, no children | 46.8% | 39.2% | 42.9% |
| Non Family Households | 12,268 | 105,912 | 43,255,233 |
| Single householder, w/children | 9.2% | 21.0% | 15.8% |
| Single householder, no children | 14.4% | 13.5% | 10.8% |