Route 154 begins at US 1 in Old Saybrook. It heads south on Great Hammock Road as it is parallel to the Long Island Sound. It becomes known as Plum Bank Road, shortly before turning eastward as Indianola Drive as it enters Knollwood. Maple Avenue turns on to Route 154 as it enters Fenwick. It passes by the Fenwick Golf Course just prior to passing over the South Cove. It becomes Bridge Street for a short time before executing a sharp turn to the west as College Street, and later Main Street.