Modern NY 12F was added to the state highway system in 1916 and designated as part of NY 3 in 1924. In the 1930 renumbering of state highways in New York, NY 3 was moved onto a new alignment to the east and its former alignment between Watertown and Clayton became NY 12E. Also assigned at this time was NY 12F, which initially used what is now NY 12E from Dexter to Watertown. The alignments of NY 12E and NY 12F east of Dexter were swapped .