New York State Route 12E (NY 12E) is a state highway located entirely within the northwestern part of Jefferson County in northern New York in the United States. The southern terminus is at NY 12F in the village of Brownville. Its northern terminus, both signed and official, is at NY 12 in the village of Clayton. While NY 12 follows a direct north–south routing between Watertown and Clayton, NY 12E diverges westward to follow the shoreline of Lake Ontario. The portion of NY 12E north of its junction with NY 180 is part of the Seaway Trail, a National Scenic Byway.

Jefferson County is a county on the northern border of the U.S. state of New York. As of the 2020 census, the population was 116,721. Its county seat is Watertown. The county is named after Thomas Jefferson, third President of the United States of America. It is adjacent to Lake Ontario, southeast from the Canada–US border of Ontario. The county is part of the North Country region of the state.