Warner developed into a prosperous farming community which produced meats, dairy goods, vegetables, hay and apples. The Warner River and its tributaries provided water power for mills, which in 1832 included 12 sawmills, 6 gristmills, a paper mill and 2 clothing factories. By 1858, there was also a cabinet manufacturer and bottle manufacturer. In 1885, industries included a bedstead factory, chain factory, woolen cloth factory, iron foundry, tannery and glove manufacturer. On September 9, 1821, the town was hit by what is known as the Norfolk and Long Island Hurricane. It leveled houses and forests in a 16 to 18 mile (27 to 30 km) long swath of destruction beginning west of Lake Sunapee, through New London and Sutton, over the southwest spur of Mount Kearsarge and ending at the Webster line. The storm killed 4 people in Warner, seriously injured others and destroyed considerable property.
Mount Kearsarge, elevation above sea level, located in the extreme north of the town, is the highest point in Warner. Two state parks are located on the mountain: Rollins State Park in Warner and Winslow State Park in Wilmot. Mount Kearsarge is a popular hiking destination, due both to its bare, rocky summit, and to the fact that a paved road climbs from Rollins State Park to within a half mile of the summit. The peak is the highest point along the Sunapee-Ragged-Kearsarge Greenway, a hiking trail which links 10 towns and encircles the Lake Sunapee region of western New Hampshire.
The town is crossed by Interstate 89 and New Hampshire Route 103. State routes 114 and 127 cross the extreme southwestern and southeastern corners of the town, respectively. Warner borders the towns of Wilmot, Andover and Salisbury to the north, Webster to the east, Hopkinton and Henniker to the south, Bradford to the west, and Sutton to the northwest.
As of the census of 2000, there were 2,760 people, 1,048 households, and 728 families residing in the town. The population density was 49.6 people per square mile (19.1/km²). There were 1,228 housing units at an average density of 22.1/sq mi (8.5/km²). The racial makeup of the town was 98.33% White, 0.04% African American, 0.25% Native American, 0.22% Asian, 0.11% from other races, and 1.05% from two or more races. Hispanic or Latino of any race were 0.72% of the population.
There were 1,048 households out of which 33.2% had children under the age of 18 living with them, 56.6% were married couples living together, 8.9% had a female householder with no husband present, and 30.5% were non-families. 25.1% of all households were made up of individuals and 8.2% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 3.01.
In the town the population was spread out with 24.5% under the age of 18, 7.9% from 18 to 24, 28.9% from 25 to 44, 26.5% from 45 to 64, and 12.2% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 98.7 males. For every 100 females age 18 and over, there were 92.0 males.
The median income for a household in the town was $44,142, and the median income for a family was $50,926. Males had a median income of $36,143 versus $25,848 for females. The per capita income for the town was $21,588. About 5.0% of families and 6.8% of the population were below the poverty line, including 11.0% of those under age 18 and 4.2% of those age 65 or over.