Route 154 was established in 1932 as a renumbering of old State Highway 338. Its original route started at US 1 in Old Saybrook Center and followed Main Street then College Street to Saybrook Point, then continued through Fenwick along Maple Avenue to end at itself just south of the town center. In 1935, a section of Maple Avenue between Summerfield Road and Main Street was redesignated Route 154A and the western part of the loop moved to the current alignment along Plum Bank Road and Great Hammock Road (former SR 603). In 1963, Route 154A was turned over to the town of Old Saybrook.