According to the U.S. Census Bureau
the county has a total area of 533 square miles (1,380 km2), of which 495 square miles (1,280 km2) is land and 37 square miles (96 km2) (7.0%) is water.
Fulton County is in the central part of the state, northwest of Albany, lying in the southern Adirondack Mountains.
Approximately 58% of the county is within the boundaries of Adirondack Park.