- Western Terminus:
- Judd Road (Oneida CR 840) and Halsey Road in Whitesboro
- Eastern Terminus:
- North-South Arterial Highway (NY 5/NY 8/NY 12) in New Hartford
- 4.02 miles
NY 840 is a short extension of the NY 8 expressway from New Hartford to Whitesboro. It begins at the point where NY 8 leaves the expressway to join NY 5/NY 12 along the North-South Arterial Highway and runs west as an expressway to Halsey Road in Whitesboro, where it becomes Judd Road (CR 840). CR 840 continues west for a few miles to end at NY 233 in Rome.