Constantia is a town in Oswego County, New York, USA. The population was 5,141 at the 2000 census.
The Town of Constantia is in the southeast part of the county.
The town was first settled around 1793 and was known then as "Rotterdam." Francis Adrian Vanderkemp and Marc Isambard Brunel were two of its citizens. The Town of Constantia was created from part of the Town of Mexico in 1808. In 1825, the town was reduced by the formation of the Town of Hastings, and was reduced again in 1839 to form the Town of West Monroe.