CT 138 History
In the 1920s, State Highway 138 went from Unionville to Canton via today's Route 4, Route 179, Maple Ave and Dowd Ave (both now SR 565) to US 44.
At the same time, modern-day Route 138 was called SH 321.
In 1932, Route 138 was commissioned between (what are now) Route 169 and Route 49. Route 138 already existed between Boston and Newport in 1928, so Connecticut used the number as a courtesy.
Some time in the 1950s, Route 138 was apparently reconstructed in the vicinity of Edmond Road in the Pachaug section of Griswold; some houses were taken. In 2003, there was discussion among officials whether the town should retain the road or abandon it (I believe this is the same section of old 138); the going sentiment was to turn it over to a private property owner who holds acreage on both sides.
In 1963, Route 138 was extended west to Route 97.