- Southern Terminus:
- New York-Connecticut state line
- Northern Terminus:
- Old Post Road (NY 35) in South Salem
- 4.67 miles
Smith Ridge Road is a north/south route extending from New Canaan, Connecticut, to South Salem, New York. It is designated CT 123 in Connecticut and becomes NY 123 upon crossing the state line. It is the easternmost north/south route in Westchester County and ends after a few miles at Old Post Road (NY 35). The entire length is a two-lane undivided road.