Constantia is a town in Oswego County, New York, United States. The population was 4,973 at the 2010 census.
According to the United States Census Bureau, the town has a total area of 99.6 square miles (258.0 km²), of which, 56.9 square miles (147.3 km²) of it is land and 42.8 square miles (110.8 km²) of it (42.93%) is water.
The south town line is the opposite shore of Oneida Lake, which is the border of Madison County, New York. The east town line is the border of Oneida County, New York.
The Erie Canal, runs through the town, using Oneida Lake as a waterway.
The north boundary is marked by the south edge of the Tug Hill Plateau.
As of the census of 2000, there were 5,141 people, 1,893 households, and 1,398 families residing in the town. The population density was 90.4 people per square mile (34.9/km²). There were 2,351 housing units at an average density of 41.3 per square mile (16.0/km²). The racial makeup of the town was 98.29% White, 0.21% Black or African American, 0.66% Native American, 0.08% Asian, 0.02% Pacific Islander, 0.08% from other races, and 0.66% from two or more races. Hispanic or Latino of any race were 0.33% of the population.
There were 1,893 households out of which 37.3% had children under the age of 18 living with them, 61.0% were married couples living together, 8.1% had a female householder with no husband present, and 26.1% were non-families. 19.0% of all households were made up of individuals and 6.0% had someone living alone who was 65 years of age or older. The average household size was 2.72 and the average family size was 3.11.
In the town, the population was spread out with 28.4% under the age of 18, 5.7% from 18 to 24, 31.5% from 25 to 44, 24.7% from 45 to 64, and 9.6% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 106.5 males. For every 100 females age 18 and over, there were 103.7 males.
The median income for a household in the town was $39,932, and the median income for a family was $45,373. Males had a median income of $31,276 versus $23,299 for females. The per capita income for the town was $15,818. About 6.2% of families and 9.5% of the population were below the poverty line, including 10.7% of those under age 18 and 3.6% of those age 65 or over.