Felts Mills is a hamlet in the town of Rutland of Jefferson County, New York, United States. The population was 372 at the 2010 census. Felts Mills' original name was Mid Road because it is the halfway point between Watertown and Carthage.Felts Mills was sited on one of several natural falls on the Black River and first settled with the construction of a grist mill in about 1800. An improved dam was erected in 1821, and a stone mill in the following year. In 1824, John Felts constructed the large sawmills that gave the town its name. In 1889, the Taggart Paper Company built a large paper mill on an island across the river, ruins of which are still visible today.