| | Chelmsford, MA | Sebastian, FL | United States |
| Population | 36,271 | 24,843 | 329,725,481 |
| Female Population | 51.7% | 50.8% | 50.5% |
| Male Population | 48.3% | 49.2% | 49.5% |
| Median Age | 42.7 | 56.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 33,900 | 21,971 | 309,327,143 |
| Population - 2000 | 33,858 | 16,181 | 285,036,114 |
| Population - 1990 | 32,383 | 10,205 | 251,960,433 |
| Pop. 2000 to Now | 4.9% | 63.7% | 15.6% |
| Pop. 1990 to Now | 9.7% | 159.5% | 30.8% |
| space4 | | | |
| Population Density | 1,621.4 | 1,827.8 | 93.4 |
| Land Area | 22.4 | 13.6 | 3,531,905.4 |
| Water Area | 0.7 | 0.8 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Chelmsford, MA | Sebastian, FL | United States |
| Age 0 to 4 | 5.5% | 2.8% | 5.9% |
| Age 5 to 9 | 6.3% | 3.6% | 6.1% |
| Age 10 to 14 | 6.0% | 4.1% | 6.6% |
| Age 15 to 17 | 3.3% | 2.6% | 3.9% |
| Age 18 to 20 | 3.1% | 1.3% | 4.0% |
| Age 21 to 24 | 4.3% | 3.1% | 5.2% |
| Age 25 to 34 | 11.5% | 8.4% | 13.8% |
| Age 35 to 44 | 12.6% | 8.1% | 12.9% |
| Age 45 to 54 | 15.3% | 13.6% | 12.6% |
| Age 55 to 59 | 8.3% | 9.0% | 6.7% |
| Age 60 to 64 | 6.5% | 8.8% | 6.3% |
| Age 65 to 74 | 10.5% | 19.2% | 9.6% |
| Age 75 to 84 | 5.0% | 11.8% | 4.5% |
| Age 85 and over | 1.8% | 3.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Chelmsford, MA | Sebastian, FL | United States |
| White | 82.0% | 87.0% | 59.4% |
| Black | 1.3% | 1.7% | 12.2% |
| Asian | 9.2% | 0.5% | 5.6% |
| Native American | 0.0% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.4% | 0.2% |
| Other | 0.7% | 0.7% | 0.4% |
| Two or More Races | 2.6% | 2.3% | 3.2% |
| Hispanic | 4.2% | 7.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Chelmsford, MA | Sebastian, FL | United States |
| Married Population | 60.3% | 58.2% | 49.8% |
| Currently Married | 59.2% | 57.4% | 48.0% |
| Married but Separated | 1.2% | 0.8% | 1.8% |
| Single Population | 39.7% | 41.8% | 50.2% |
| Never Married | 27.1% | 19.7% | 33.8% |
| Divorced | 8.0% | 12.9% | 10.8% |
| Widowed | 4.5% | 9.2% | 5.6% |
| space5 | | | |
| Household Size | 2.65 | 2.33 | 2.60 |
| Households | 13,628 | 10,659 | 124,010,992 |
| Family Households | 9,865 | 6,813 | 80,755,759 |
| Married couple, w/children | 36.9% | 15.6% | 30.5% |
| Married couple, no children | 47.4% | 70.9% | 42.9% |
| Non Family Households | 3,763 | 3,846 | 43,255,233 |
| Single householder, w/children | 8.2% | 6.1% | 15.8% |
| Single householder, no children | 7.5% | 7.4% | 10.8% |