| | St. Leonard, MD | Billerica, MA | United States |
| Population | 454 | 41,995 | 329,725,481 |
| Female Population | 48.7% | 49.1% | 50.5% |
| Male Population | 51.3% | 50.9% | 49.5% |
| Median Age | 45.7 | 43 | 38.4 |
| space3 | | | |
| Population - 2010 | 918 | 40,419 | 309,327,143 |
| Population - 2000 | 536 | 38,981 | 285,036,114 |
| Population - 1990 | 609 | 37,609 | 251,960,433 |
| Pop. 2000 to Now | -12.1% | 10.4% | 15.6% |
| Pop. 1990 to Now | -22.7% | 14.4% | 30.8% |
| space4 | | | |
| Population Density | 198.7 | 1,642.6 | 93.4 |
| Land Area | 2.3 | 25.6 | 3,531,905.4 |
| Water Area | 0.0 | 0.7 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Leonard, MD | Billerica, MA | United States |
| Age 0 to 4 | 0.0% | 4.0% | 5.9% |
| Age 5 to 9 | 5.3% | 4.4% | 6.1% |
| Age 10 to 14 | 11.2% | 5.5% | 6.6% |
| Age 15 to 17 | 0.0% | 4.1% | 3.9% |
| Age 18 to 20 | 3.7% | 2.8% | 4.0% |
| Age 21 to 24 | 2.6% | 4.7% | 5.2% |
| Age 25 to 34 | 0.0% | 14.4% | 13.8% |
| Age 35 to 44 | 23.6% | 12.9% | 12.9% |
| Age 45 to 54 | 26.9% | 15.2% | 12.6% |
| Age 55 to 59 | 6.8% | 8.7% | 6.7% |
| Age 60 to 64 | 5.3% | 7.1% | 6.3% |
| Age 65 to 74 | 8.6% | 10.1% | 9.6% |
| Age 75 to 84 | 5.9% | 4.3% | 4.5% |
| Age 85 and over | 0.0% | 1.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Leonard, MD | Billerica, MA | United States |
| White | 86.1% | 79.6% | 59.4% |
| Black | 1.5% | 6.2% | 12.2% |
| Asian | 0.0% | 7.2% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.0% | 0.6% | 0.4% |
| Two or More Races | 2.9% | 1.9% | 3.2% |
| Hispanic | 9.5% | 4.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Leonard, MD | Billerica, MA | United States |
| Married Population | 77.6% | 52.8% | 49.8% |
| Currently Married | 77.6% | 51.3% | 48.0% |
| Married but Separated | 0.0% | 1.5% | 1.8% |
| Single Population | 22.4% | 47.2% | 50.2% |
| Never Married | 16.6% | 33.4% | 33.8% |
| Divorced | 0.0% | 8.9% | 10.8% |
| Widowed | 5.8% | 4.9% | 5.6% |
| space5 | | | |
| Household Size | 2.44 | 2.63 | 2.60 |
| Households | 186 | 15,498 | 124,010,992 |
| Family Households | 160 | 11,352 | 80,755,759 |
| Married couple, w/children | 45.0% | 33.2% | 30.5% |
| Married couple, no children | 45.6% | 44.2% | 42.9% |
| Non Family Households | 26 | 4,146 | 43,255,233 |
| Single householder, w/children | 0.0% | 7.2% | 15.8% |
| Single householder, no children | 9.4% | 15.5% | 10.8% |