The primary settlement in town, where over 66% of the population resides, is defined by the U.S. Census Bureau as the Derry census-designated place (CDP) and includes the densely-populated portions of the town centered on the intersection of New Hampshire Route 28 and New Hampshire Route 102.
As of the census of 2000, there were 34,021 people, 12,327 households, and 8,789 families residing in the town. The population density was 950.7 people per square mile (367.0/km²). There were 12,735 housing units at an average density of 137.4 persons/km² (355.9 persons/sq mi). The racial makeup of the town was 96.05% White, 0.90% African American, 0.21% Native American, 1.06% Asian, 0.05% Pacific Islander, 0.60% from other races, and 1.13% from two or more races. 1.89% of the population were Hispanic or Latino of any race.
There were 12,327 households out of which 42.6% had children under the age of 18 living with them, 56.4% were married couples living together, 10.6% have a woman whose husband does not live with her, and 28.7% were non-families. 21.6% of all households were made up of individuals and 4.9% had someone living alone who was 65 years of age or older. The average household size was 2.74 and the average family size was 3.24.
In the town the population was spread out with 30.1% under the age of 18, 7.4% from 18 to 24, 35.5% from 25 to 44, 20.7% from 45 to 64, and 6.2% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 98.6 males. For every 100 females age 18 and over, there were 96.6 males.
The median income for a household in the town was $54,634, and the median income for a family was $61,625. Males had a median income of $41,271 versus $30,108 for females. The per capita income for the town was $22,315. 4.6% of the population and 3.3% of families were below the poverty line. Out of the total people living in poverty, 5.0% are under the age of 18 and 7.1% are 65 or older.
As of the census of 2000, there were 22,661 people, 8,670 households, and 5,739 families residing in the CDP (census-designated place), the urban center of Derry. The population density was 1,469.3 people per square mile (567.4/km²). There were 8,942 housing units at an average density of 223.9 persons/km² (579.8 persons/sq mi). The racial makeup of the town was 95.58% White, 1.05% African American, 0.22% Native American, 1.12% Asian, 0.02% Pacific Islander, 0.75% from other races, and 1.26% from two or more races. 2.21% of the population were Hispanic or Latino of any race.
There were 8,670 households out of which 39.2% had children under the age of 18 living with them, 49.7% were married couples living together, 12.0% have a woman whose husband does not live with her, and 33.8% were non-families. 26.0% of all households were made up of individuals and 6.1% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.18.
In the CDP the population was spread out with 29.0% under the age of 18, 8.1% from 18 to 24, 35.9% from 25 to 44, 19.9% from 45 to 64, and 7.1% who were 65 years of age or older. The median age was 33 years. For every 100 females there were 97.6 males. For every 100 females age 18 and over, there were 94.7 males.
The median income for a household is $49,792, and the median income for a family was $56,332. Males had a median income of $40,185 versus $28,580 for females. The per capita income for the town was $21,938. 6.0% of the population and 4.3% of families were below the poverty line. Out of the total people living in poverty, 6.9% are under the age of 18 and 7.6% are 65 or older.