| | Mount Rainier, MD | Brentwood, MD | United States |
| Population | 8,290 | 3,775 | 329,725,481 |
| Female Population | 50.3% | 51.0% | 50.5% |
| Male Population | 49.8% | 49.0% | 49.5% |
| Median Age | 40.8 | 33.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 7,835 | 3,322 | 309,327,143 |
| Population - 2000 | 8,498 | 2,844 | 285,036,114 |
| Population - 1990 | 7,954 | 3,005 | 251,960,433 |
| Pop. 2000 to Now | -4.5% | 20.9% | 15.6% |
| Pop. 1990 to Now | 2.1% | 14.4% | 30.8% |
| space4 | | | |
| Population Density | 13,034.6 | 9,805.2 | 93.4 |
| Land Area | 0.6 | 0.4 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Mount Rainier, MD | Brentwood, MD | United States |
| Age 0 to 4 | 5.2% | 8.9% | 5.9% |
| Age 5 to 9 | 5.3% | 7.2% | 6.1% |
| Age 10 to 14 | 3.2% | 7.6% | 6.6% |
| Age 15 to 17 | 4.1% | 3.7% | 3.9% |
| Age 18 to 20 | 3.8% | 1.9% | 4.0% |
| Age 21 to 24 | 4.7% | 4.9% | 5.2% |
| Age 25 to 34 | 13.8% | 18.8% | 13.8% |
| Age 35 to 44 | 18.6% | 15.0% | 12.9% |
| Age 45 to 54 | 15.0% | 12.6% | 12.6% |
| Age 55 to 59 | 5.3% | 4.7% | 6.7% |
| Age 60 to 64 | 9.0% | 4.7% | 6.3% |
| Age 65 to 74 | 10.0% | 6.4% | 9.6% |
| Age 75 to 84 | 1.1% | 2.7% | 4.5% |
| Age 85 and over | 1.0% | 0.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Mount Rainier, MD | Brentwood, MD | United States |
| White | 18.7% | 11.3% | 59.4% |
| Black | 47.4% | 29.0% | 12.2% |
| Asian | 1.2% | 1.7% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.5% | 0.0% | 0.4% |
| Two or More Races | 1.3% | 3.0% | 3.2% |
| Hispanic | 30.9% | 55.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Mount Rainier, MD | Brentwood, MD | United States |
| Married Population | 44.3% | 40.2% | 49.8% |
| Currently Married | 42.6% | 39.4% | 48.0% |
| Married but Separated | 1.7% | 0.8% | 1.8% |
| Single Population | 55.7% | 59.8% | 50.2% |
| Never Married | 42.8% | 46.5% | 33.8% |
| Divorced | 8.1% | 9.9% | 10.8% |
| Widowed | 4.9% | 3.4% | 5.6% |
| space5 | | | |
| Household Size | 1.99 | 2.91 | 2.60 |
| Households | 4,163 | 1,298 | 124,010,992 |
| Family Households | 1,888 | 794 | 80,755,759 |
| Married couple, w/children | 29.9% | 35.0% | 30.5% |
| Married couple, no children | 45.4% | 23.7% | 42.9% |
| Non Family Households | 2,275 | 504 | 43,255,233 |
| Single householder, w/children | 15.1% | 23.3% | 15.8% |
| Single householder, no children | 9.6% | 18.0% | 10.8% |