Route 64 is part of the old US 6A, and was designated in 1967.

In the 1920s, this road was part of New England Interstate Route NE-3, a road leading from New York State to Cape Cod. Most of NE-3 became part of US 6 in 1927, but the route from Woodbury to Waterbury remained part of NE-3.

Old Sherman Hill Road is the original route in Woodbury and Middlebury. In 1931, the state opened about 3 miles of highway on new alignment: today's Sherman Hill Road and Route 64. Near the Middlebury town line, the new road overpasses the old one.

On Jan. 1, 1932, during the Great Renumbering, today's Route 64 became part of the original Route 14, which extended nearly 90 miles inside the state, from Woodbury to Sterling. On Jan. 1, 1941, Route 14 from Woodbury to Willimantic was designated US 6A, to provide an alternate to US 6.

In the mid-1960s, as Interstate 84 was being constructed through Waterbury, the state Highway Department proposed another route number change, to better reflect the evolving highway system. US 6A east of I-84, from Southington to Willimantic, would become the new Route 66. US 6A through Waterbury, a route duplicated by the new I-84, would no longer be signed. The section to the west, leading to Woodbury, would be given another available route number: 64. The proposed changes were announced in late 1965, and took place in 1967.

Route 64 freeway (ok, a bypass); still would have been cool

Between the vicinity of Route 63 and I-84 in Middlebury, Route 64 serves heavy traffic. The incomplete interchange at I-84 and Route 63, with access to and from the west only, contributes to this: traffic to and from Waterbury uses Route 64 to access I-84.

In 1973, proposals from the town of Middlebury and the Central Naugatuck Council of Governments included a bypass for Route 64, running south of the current alignment, between Rose Court and Woodside Avenue. The bypass would include an interchange at Route 63. This was never implemented, but the town's 2001 development plan draft still included the bypass as a regional priority. Completing the Route 63/I-84 interchange is also proposed as a way to relieve Route 64 traffic.

Middlebury Greenway: an old trolley line

About 4.5 miles of Route 64, from Quassy Amusement & Waterpark to Route 63, parallels the Middlebury Greenway, a former trolley line converted to a trail. Starting in 1908, the electrified line connected Middlebury and Woodbury. After the state upgraded the road next to the line, more people chose to drive to the park, and the trolley closed in 1930.