Constantia is a town in Oswego County, New York, United States.

Francis Adrian Vanderkemp and Marc Isambard Brunel were two of its citizens.

The southern town line is the opposite shore of Oneida Lake, which is the border of Madison County.

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.