Lyon Mountain is a mountain located in Clinton County, New York, of which its peak is the highest point. The mountain is named for Nathaniel Lyon, an early settler of the area who moved from Vermont in 1803 and died circa 1850. Lyon Mountain stands within the watershed of the Saint Lawrence River, and into the Gulf of Saint Lawrence. The northeast slopes of Lyon Mtn. drain into Chazy Lake, the source of the Great Chazy River, and Lake Champlain, which drains into Canada's Richelieu River, thence into the Saint Lawrence River. The southeast slopes of Lyon Mtn. drain into Smithkill Brook, thence into True Brook, the Saranac River, and Lake Champlain. The southwest end of Lyon drains into Cold Brook, thence into the North Branch of the Saranac River. The west slopes of Lyon drain into Standish Brook, thence into Middle Kiln Brook, Upper and Lower Chateaugay Lakes, the source of the Chateaugay River, which drains into the Saint Lawrence River in Canada. The northwest slopes of Lyon drain into Separator Brook, thence into Upper Chateaugay Lake. Lyon Mountain Mountain Fire Observation Station, built in 1917, still stands atop the mountain, and can be accessed by hikers. Lyon Mountain is within New York's Adirondack Park.