The Town of Charleston is on the south border of the county and is southwest of the City of Amsterdam.
Charleston is the only town in the county not bordering the Mohawk River.
Parts of Charleston were in Corry's Patent (1637), Stone Heap Patent (1770), and Thomas Machin's Patent (1787). Settlers began arriving before the American Revolution.
The Town of Charleston was formed by a division of the original "Town of Mohawk" in 1793. This division, which also created the Town of Florida, terminated Mohawk as a town until another town with that name (Mohawk) was created in 1837. Charleston was reduced in size in 1823, when the Towns of Glen and Root (in part) were established.