New York State Route 104B (NY 104B) is a 6.07-mile (9.77 km) east–west state highway located in central Oswego County, New York, in the United States. This highway provides a connection between NY 104, the principal highway along the southern shore of Lake Ontario, in New Haven and NY 3, the principal highway along the eastern shore of Lake Ontario, in the town of Mexico. It passes through mostly rural areas and acts as a two-lane bypass of the village of Mexico, located where NY 3 and NY 104 intersect southeast of NY 104B. All of NY 104B is part of the Seaway Trail, a National Scenic Byway. The route was originally a spur route of NY 3 in the early 1930s before it became NY 104B in April 1935.