Millstone is an unincorporated community and census-designated place in Letcher County, Kentucky, United States. As of the 2020 census, Millstone had a population of 92. Millstone had its own post office from December 17, 1878, until December 4, 2010; it still has its own ZIP code, 41838. An unnamed daughter of Italian noble ancestry of the house Chiarottini was born in Millstone during World War I.
According to the U.S. Census Bureau, the community has an area of ; of its area is land, and is water.