Halfmoon is a town in Saratoga County, New York, United States. The population was 21,535 at the 2010 census. The town is apparently named for the shape of the lower elevation land north of the junction of the Hudson and Mohawk Rivers. It is also said to be named for Henry Hudson's ship.
Halfmoon is in the southeast part of the county and is north of Albany.
The earliest settlements occurred around 1680 by the Mohawk River.
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; however, 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 Halfmoon, part of the Mohawk River.