| | Bethlehem, PA | South Plainfield, NJ | United States |
| Population | 75,599 | 24,251 | 329,725,481 |
| Female Population | 52.2% | 50.0% | 50.5% |
| Male Population | 47.9% | 50.0% | 49.5% |
| Median Age | 36.4 | 41.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 74,974 | 23,387 | 309,327,143 |
| Population - 2000 | 71,329 | 21,810 | 285,036,114 |
| Population - 1990 | 71,428 | 20,489 | 251,960,433 |
| Pop. 2000 to Now | 5.8% | 9.9% | 15.6% |
| Pop. 1990 to Now | 5.7% | 17.0% | 30.8% |
| space4 | | | |
| Population Density | 3,955.0 | 2,923.2 | 93.4 |
| Land Area | 19.1 | 8.3 | 3,531,905.4 |
| Water Area | 0.3 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Bethlehem, PA | South Plainfield, NJ | United States |
| Age 0 to 4 | 5.0% | 6.3% | 5.9% |
| Age 5 to 9 | 4.4% | 4.8% | 6.1% |
| Age 10 to 14 | 5.2% | 5.2% | 6.6% |
| Age 15 to 17 | 3.0% | 3.9% | 3.9% |
| Age 18 to 20 | 8.7% | 2.7% | 4.0% |
| Age 21 to 24 | 7.5% | 4.1% | 5.2% |
| Age 25 to 34 | 14.6% | 15.2% | 13.8% |
| Age 35 to 44 | 11.7% | 13.6% | 12.9% |
| Age 45 to 54 | 10.6% | 12.9% | 12.6% |
| Age 55 to 59 | 5.5% | 7.6% | 6.7% |
| Age 60 to 64 | 5.8% | 6.4% | 6.3% |
| Age 65 to 74 | 9.8% | 10.6% | 9.6% |
| Age 75 to 84 | 5.2% | 4.6% | 4.5% |
| Age 85 and over | 3.0% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Bethlehem, PA | South Plainfield, NJ | United States |
| White | 55.8% | 52.5% | 59.4% |
| Black | 8.2% | 12.1% | 12.2% |
| Asian | 2.9% | 13.6% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.7% | 0.4% |
| Two or More Races | 2.6% | 3.0% | 3.2% |
| Hispanic | 30.1% | 18.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Bethlehem, PA | South Plainfield, NJ | United States |
| Married Population | 37.6% | 59.1% | 49.8% |
| Currently Married | 35.4% | 58.6% | 48.0% |
| Married but Separated | 2.2% | 0.5% | 1.8% |
| Single Population | 62.4% | 40.9% | 50.2% |
| Never Married | 45.0% | 29.6% | 33.8% |
| Divorced | 10.9% | 5.9% | 10.8% |
| Widowed | 6.6% | 5.4% | 5.6% |
| space5 | | | |
| Household Size | 2.33 | 2.94 | 2.60 |
| Households | 29,874 | 8,144 | 124,010,992 |
| Family Households | 16,673 | 6,621 | 80,755,759 |
| Married couple, w/children | 19.4% | 38.0% | 30.5% |
| Married couple, no children | 43.5% | 45.0% | 42.9% |
| Non Family Households | 13,201 | 1,523 | 43,255,233 |
| Single householder, w/children | 21.5% | 7.6% | 15.8% |
| Single householder, no children | 15.6% | 9.4% | 10.8% |