The town was formed from parts of the Towns of Greenfield and Northumberland in 1801. The Town of Corinth was taken from Hadley in 1818, and the Town of Day was removed in 1819, bringing the Town of Hadley to its current dimensions.
In 1930, the Conklingville Dam by the west town line helped create the Sacandaga Reservoir and controlled flooding.
According to the United States Census Bureau, the town has a total area of 41.1 square miles (106 km2), of which 39.8 square miles (103 km2) is land and 1.3 square miles (3.4 km2) (3.26%) is water.
The town is located within the Adirondack Park. The northern and eastern town lines are the border of Warren County.
A small part of the eastern end of the Great Sacandaga Lake (formerly the "Sacandaga Reservoir") is by the western town line and the Sacandaga River divides the town laterally and enters the Hudson River by the eastern town boundary.
As of the census[6] of 2000, there were 1,971 people, 730 households, and 538 families residing in the town. The population density was 49.6 inhabitants per square mile (19.2/km2). There were 990 housing units at an average density of 24.9 per square mile (9.6/km2). The racial makeup of the town was 97.77% White, 1.01% African American, 0.20% Native American, 0.15% Asian, 0.05% from other races, and 0.81% from two or more races. Hispanic or Latino of any race were 0.15% of the population.
There were 730 households, out of which 35.1% had children under the age of 18 living with them, 57.8% were married couples living together, 10.4% had a female householder with no husband present, and 26.3% were non-families. 19.3% of all households were made up of individuals, and 7.8% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.04.
In the town, the population was spread out, with 26.2% under the age of 18, 8.0% from 18 to 24, 29.5% from 25 to 44, 22.4% from 45 to 64, and 13.9% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 99.1 males. For every 100 females age 18 and over, there were 95.7 males.
The median income for a household in the town was $38,150, and the median income for a family was $42,438. Males had a median income of $35,694 versus $21,810 for females. The per capita income for the town was $17,560. About 6.1% of families and 9.2% of the population were below the poverty line, including 11.9% of those under age 18 and 9.9% of those age 65 or over.
Communities and locations in Hadley
Bell Brook Pond – A small artificial lake by the western town line.
Hadley – The hamlet of Hadley is near the eastern town line and the mouth of the Sacandaga River at the junction of County Roads 1 and 4..
Lynnwood – A hamlet in the western part of the town at the junction of County Roads 7 and 8.
Mount Anthony – The highest peak in the town, in its southeastern corner.
