Lyon Mountain is a hamlet and census-designated place located in the town of Dannemora in Clinton County, New York, United States.

[2] The northern slopes of Lyon Mountain are in the southern part of the community, with the 3,840-foot (1,170 m) summit to the south in the town of Saranac.

The Lyon Mountain Correctional Facility, a minimum security prison, was located in the community.

The facility closed in 2011, and has been purchased by a Canadian who has mined sand for hydrofracking from the site.

[3] According to the United States Census Bureau, the CDP has a total area of 10.2 square miles (26.3 km2), all land.

Lyon Mountain's iron ore was considered the best in the industry and was the material of choice for John Roebling and Sons in the construction of the Brooklyn Bridge.