- Southern Terminus:
- Boston Post Road (US 1) in Darien
- Northern Terminus:
- New York-Connecticut state line
- 9.41 miles
CT 124 is a north/south routes through Darien and New Canaan in western Connecticut. It begins at Boston Post Road (US 1), just north of the Connecticut Turnpike (I-95), and runs north. It ends at the New York-Connecticut state line. The entire length is a two-lane undivided road with traffic lights. CT 124 is multiplexed with CT 106 for a short distance in New Canaan.
At the New York border, CT 124 becomes Westchester Avenue, which was designated NY 137A as of 1943. It was renumbered NY 394 by 1950 and then later decommissioned. Today, Westchester Avenue exists as an unnumbered road from CT 124 at the state line to High Ridge Road (NY 137) in Pound Ridge.