The modern Route 139 was created in 1932, and was not always as short as it is now. The original route extended 8.03 miles, from US 1 to Route 15 (now Route 17) in North Branford.
In 1951, the state created Route 22 from three existing routes to help guide drivers from the new Wilbur Cross Parkway to US 1. Route 22 absorbed most of Route 139, leaving the 2-mile segment we see today.
In 1964, the short Route 139A (dead end section of Branford Road) was turned over to the town.