Henderson is a town in Jefferson County, New York, United States. The population was 1,360 at the 2010 census. The town is named after William Henderson, the original European-American land owner.
According to the United States Census Bureau, the town has a total area of 52.9 square miles (137.1 km), of which 41.2 square miles (106.7 km) are land and 11.7 square miles (30.4 km), or 22.21%, are water. The west boundary of the town is Lake Ontario.
New York State Route 3 is a north-south highway. New York State Route 178 is an east-west highway, which intersects NY-3 at Aspinwall Corners.
As of the census of 2000, there were 1,377 people, 577 households, and 406 families residing in the town. The population density was 33.3 people per square mile (12.9/km²). There were 1,557 housing units at an average density of 37.7 per square mile (14.5/km²). The racial makeup of the town was 98.69% White, 0.22% Native American, 0.58% from other races, and 0.51% from two or more races. Hispanic or Latino of any race were 0.65% of the population.
There were 577 households out of which 23.2% had children under the age of 18 living with them, 59.3% were married couples living together, 6.2% had a female householder with no husband present, and 29.6% were non-families. 23.9% 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 2.39 and the average family size was 2.76.
In the town, the population was spread out with 20.3% under the age of 18, 6.7% from 18 to 24, 24.3% from 25 to 44, 29.8% from 45 to 64, and 19.0% who were 65 years of age or older. The median age was 44 years. For every 100 females, there were 100.4 males. For every 100 females age 18 and over, there were 103.3 males.
The median income for a household in the town was $37,019, and the median income for a family was $45,357. Males had a median income of $32,050 versus $24,792 for females. The per capita income for the town was $20,071. About 8.1% of families and 11.1% of the population were below the poverty line, including 8.7% of those under age 18 and 5.6% of those age 65 or over.