|• Total||51.4 sq mi (133.1 km2)|
|• Land||51.4 sq mi (133.0 km2)|
|• Water||0.0 sq mi (0.1 km2)|
|Elevation||1,033 ft (315 m)|
|• Density||58.0/sq mi (22.4/km2)|
|Time zone||Eastern (EST) (UTC-5)|
|• Summer (DST)||EDT (UTC-4)|
|GNIS feature ID||1462232|
According to the United States Census Bureau, the town has a total area of 51.4 mi2 (133.1 km2), of which 51.3 mi2 (133.0 km2) is land and 0.1 mi2 (0.1 km2) (0.10%) is water.
Underhill Independent Elementary school tested best in the county in reading proficiency in the New England Common Assessment Program test in 2008. Underhill Central stood first in math proficiency.
As of the census of 2000, there were 2,980 people, 1,055 households, and 853 families residing in the town. The population density was 58.0 people per square mile (22.4/km2). There were 1,088 housing units at an average density of 21.2 per square mile (8.2/km2). The racial makeup of the town was 98.49% White, 0.27% African American, 0.13% Native American, 0.20% Asian, 0.30% from other races, and 0.60% from two or more races. Hispanic or Latino of any race were 0.70% of the population.
There were 1,055 households out of which 42.0% had children under the age of 18 living with them, 73.0% were married couples living together, 4.9% had a female householder with no husband present, and 19.1% were non-families. 13.6% of all households were made up of individuals and 3.9% had someone living alone who was 65 years of age or older. The average household size was 2.82 and the average family size was 3.13.
In the town the population was spread out with 29.0% under the age of 18, 4.6% from 18 to 24, 32.6% from 25 to 44, 28.2% from 45 to 64, and 5.7% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 101.9 males. For every 100 females age 18 and over, there were 99.8 males.
The median income for a household in the town was $66,492, and the median income for a family was $69,837. Males had a median income of $46,949 versus $29,336 for females. The per capita income for the town was $26,746. About 2.8% of families and 5.2% of the population were below the poverty line, including 8.9% of those under age 18 and 1.7% of those age 65 or over.
- Thomas Cale, non-voting congressman from the District of Alaska
- Pat Dealy, catcher with the St. Paul Saints, Boston Beaneaters, Washington Nationals, and Syracuse Stars
- Bernard Joseph Leddy, US federal judge
- Richard Phillips, a merchant mariner, who resides in Underhill, whose ship, the Maersk Alabama, was hijacked by Somali pirates in 2009. The story was later adapted into a film, Captain Phillips.
- "American FactFinder". United States Census Bureau. Retrieved 2008-01-31.
- "US Board on Geographic Names". United States Geological Survey. 2007-10-25. Retrieved 2008-01-31.
- Walsh, Molly (January 29, 2009). NECAP:Student scores improve. Burlington Free Press.