- Western Terminus:
- Oxford Road (CT 67) in Oxford
- Eastern Terminus:
- South Main Street (CT 10) in Cheshire
- 13.58 miles
- New Haven
CT 42 is an east/west route extending from Oxford to Cheshire. It begins at Oxford Road (CT 67) and follows Chestnut Tree Hill Road and Pines Bridge Road to Beacon Falls, where there is an interchange with the CT 8 expressway. On the other side of the expressway, it is a four-lane divided highway called South Main Street, which curves to the north. CT 42 then turns east onto Bethany Road.
Bethany Road runs east for about a mile and then ends. CT 42 turns onto Munson Road, which becomes Lasky Road and then Beacon Road before ending at Litchfield Turnpike (SR 703). CT 42 turns north onto Litchfield Turnpike for one block to where it ends at Amity Road (CT 63). The two routes are multiplexed for one block, and then CT 42 splits off onto Cheshire Road, which changes names to become Mountain Road and then Bethany Mountain Road. At the end of Bethany Mountain Road, CT 42 turns onto North Brooksvale Road and follows it to Cheshire, where it ends at South Main Street (CT 10).