The western terminus of the route is at US 6 roughly 2 miles (3.2 km) northwest of Brewster, and the eastern is in the hamlet of Sears Corners.

NY 312 begins at US 6 in Southeast, New York just northeast of Middle Branch Reservoir, one of the many reservoirs in Putnam County which supply New York City's large need for drinking water.

The route heads northeast, before veering to the north after a 0.5 mile (0.8 km) to bypass a hill 680 feet (210 m) high.

[3] Past the hill, the route curves eastward then northeastward as it meets I-84 by way of an interchange and approaches the hamlet of Dykemans.

Just north of the station, NY 312 turns almost due east as it crosses the Harlem Line at-grade and exits Dykemans.