The Town of Halfmoon is in the southeast part of the county and is north of Albany.
The town was formed while still part of Albany County in 1788. The name was briefly changed to "Orange" when the Town of Waterford was created in 1816 from part of Halfmoon, but the current name was restored in 1820. In 1828, the western portion of the town was used to create the Town of Clifton Park.
The Erie Canal was built along the south part of Half Moon, part of the Mohawk River.
In 1859, the community of Mechanicville set itself off from the town by incorporating as a village and became a city in 1910.
The south town line, delineated by the Mohawk River, is the border of Albany County. The east town line, at the Hudson River, is the border of Rensselaer County. The north town line is marked by Anthony Kill, a tributary of the Hudson River.
Interstate 87, the Adirondack Northway, is a multilane north-south expressway along the western edge of Half Moon. US Route 9 parallels the Interstate farther to the east. New York State Route 146, an east-west highway, intersects US-9 at Clifton Park village. US Route 4 is a north-south highway in the eastern part of the town. New York State Route 236 is a short state highway linking NY-146 to US-9.
There were 7,778 households out of which 30.3% had children under the age of 18 living with them, 49.9% were married couples living together, 9.0% had a female householder with no husband present, and 37.5% were non-families. 29.1% of all households were made up of individuals and 7.1% had someone living alone who was 65 years of age or older. The average household size was 2.35 and the average family size was 2.93.
In the town the population was spread out with 23.7% under the age of 18, 6.9% from 18 to 24, 36.3% from 25 to 44, 22.5% from 45 to 64, and 10.6% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 94.7 males. For every 100 females age 18 and over, there were 91.4 males.
The median income for a household in the town was $46,234, and the median income for a family was $53,515. Males had a median income of $40,076 versus $30,512 for females. The per capita income for the town was $23,714. About 3.7% of families and 4.5% of the population were below the poverty line, including 5.6% of those under age 18 and 6.4% of those age 65 or over.