It starts at US 1 in East Haven and ends at US 1 in Branford, running for 4.27 miles (6.87 km).

It heads south, intersecting with Route 100 (Main Street) in the downtown area, and then turns eastward about 0.7 miles (1.1 km) later along Short Beach Road.

Route 142 goes through the southern part of East Haven as it heads towards the village of Short Beach.

After crossing the Farm River into the town of Branford, the road becomes known as Shore Drive.

[1] The section of Route 142 in Branford from Double Beach Road to the eastern terminus is designated the "William E. Keish, Jr. Memorial Highway",[2] named after a Connecticut Department of Transportation official.