Three Mile Bay is a community (and census-designated place) located in Jefferson County, New York. The elevation there is 259 feet. It was settled between 1810 and 1820. Early resident Asa Wilcox built 48 brigs, propellers, schooners, and other seafaring vessels from 1835 to 1853. Some of these vessels like the A.E. Vickery, ultimately joined the more than 500 shipwrecked vessels now resting at the bottom of the St. Lawrence River and Lake Ontario.
The hamlet has its own post office, a volunteer fire company, and boat launches for fishing and recreation in the various outlying bays that draw from Lake Ontario and the St. Lawrence seaway.