Leonardsville is a hamlet on the Unadilla River in the Town of Brookfield in Madison County, New York, United States. A portion of it does also extend into the Town of Plainfield in Otsego County, New York, United States.
The community started as a number of small factories deriving power from a dam on the Unadilla River during the first decade of the 19th century. These were known locally as the shops and included a scythe and hoe factory, a blacksmith shop, a grist mill, a saw mill, a horse rake factory and wagon shop, and a foundry and machine shop.