Shortly after they arrived, they purchased a piece of land from the local Pennacook tribal chief Cutshamache for the price of "six pounds of currency and a coat" and on the condition that Roger, a local Pennacook man, would still be allowed to plant his corn and take alewives from a local water source. Roger's Brook, a small stream which cuts through the eastern part of town, is named in his honor. In May 1646 the settlement was incorporated as a town and was named Andover. This name was likely chosen in honor of the town of Andover in England, which was near the original home of some of the first residents. The first recorded town meeting was held in 1656 in the home of settler John Osgood.

The old burying ground in what is now North Andover marks the center of the early town. Contrary to popular belief, the towns split due to the location of the Old North Church, also located in what is now North Andover. So technically, what is now Andover was not incorporated as a township until many years after 1646. The villagers from the southwestern part of the town were tired of walking all the way to the extreme north of what was then Andover, and decided to build their own church central to what is now Andover. Logically you would think the northern part of the town would keep the name Andover, due to their higher stake of villagers, but fights and quibbles throughout the church and town meetings ultimately led to the elder part of town being known as what is now North Andover. Early on the general populace was concentrated together around the Old Center (North Andover) for protection from feared Indian attacks, but the Indians were fairly peaceful until the outbreak of King Philip's War in 1675. King Philip was an Indian who organized a revolt against the white settlers throughout most of New England. Six Indian raids occurred between 1676 and 1698 until ever-increasing numbers of white settlers established control of the land.

As of the census of 2000, there were 31,247 people, 11,305 households, and 8,490 families residing in the town. The population densitywas 1,007.8 people per square mile (389.1/km²). There were 11,590 housing units at an average density of 144.3 persons/km² (373.8 persons/sq mi). The racial makeup of the town was 91.60% White, 0.75% African American, 0.06% Native American, 5.73% Asian, 0.04% Pacific Islander, 0.84% from other races, and 0.99% from two or more races. 1.81% of the population were Hispanic or Latino of any race.

There are 11,305 households out of which 40.3% have children under the age of 18 living with them, 65.6% were married couples living together, 7.5% have a woman whose husband does not live with her, and 24.9% were non-families. 21.6% of all households were made up of individuals and 9.2% 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 28.8% under the age of 18, 4.7% from 18 to 24, 27.5% from 25 to 44, 26.8% from 45 to 64, and 12.3% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 92.9 males. For every 100 females age 18 and over, there were 87.9 males.

According to a 2007 estimate^[3], the median income for a household in the town was $102,762, and the median income for a family was $131,469. Males with full-time year-round jobs had a median income higher than $100,000; for females, the median was $62,649. The per capita income for the town was $45,422. 1.9% of families and 2.7% of the population, including 3.7% of people aged under 18 years and 4% of people aged 65 and over, were below the poverty line.