Before the 1932 renumbering
In the 1920s, State Highway 123 was an east-west route from Cornwall to Canton:
- today's Route 4, from US 7 to Torrington
- former Route 4 (mostly today's US 202), from Torrington to Canton via Collinsville
At that time, present-day Route 123 north of New Canaan was called SH 184, and south of there, SH 302.
Norwalk Road (today's Route 123) was the first major road in New Canaan, connecting the town to Norwalk Harbor. In 1925, Norwalk officials submitted a bill to add a state highway along this road: from Nash's Corner in Norwalk via New Canaan Center and Selleck's Corners (Route 124 at West Road) in New Canaan to New York. This route is fairly close to the Route 29 shown on the 1932 highway map.
In 1931, New Canaan residents were asked to vote on the alignment of a new state highway leading from the town center to New York State. The route from Norwalk (along New Canaan and Norwalk roads) had already been established. The alternatives were:
- present Smith Ridge Road (today's Route 123, leading to Ridgefield and Danbury via New York)
- Oenoke Avenue (today's Route 124)
- A new road, splitting into a Y at the north end, leading to Pinney's corner and Smith Ridge Road.
The Smith Ridge route narrowly beat out the new route, and soundly beat the Route 124 option.
Modern Route 123
Today's Route 123 was commissioned in 1932. Its original alignment, from south to north:
- Mansfield Avenue in Darien (today's Route 124) leading to the New Canaan town line
- South Avenue and Cherry Street in New Canaan (also part of Route 124)
- Forest Street to Smith Ridge Road (now a local street)
- Smith Ridge Road to the state line (also part of today's Route 123)
In other words, Route 123 started in Darien, crossed Route 29 in New Canaan, and continued to the state line.
In 1933, work was in progress to relocate Route 29 to a 2-mile "Norwalk - New Canaan Cutoff", which is now called New Norwalk Road. Since the new road bypasses downtown New Canaan to merge with Route 123, it made more sense, for route continuity, for routes 29 and 123 to switch places south of there. (Switching to the south also maintained consistency at the New York border.)
The result: routes 29 and 123 no longer intersected, and Route 123 started in Norwalk instead of Darien.
In 1962, the state intended to spend more than $200,000 planning and surveying the Smith Ridge Road stretch of Route 123 north of New Canaan center; that road was said to be heavily traveled and poorly constructed.
In 1970, Route 123 was moved from Riverside Avenue to Main Street in downtown Norwalk. This was one of several road changes resulting from US 7 freeway construction; that route opened in 1971. The leftover portion of Route 123 became SR 809.
In the 1980s Route 123 was for a time known as Beer Can Boulevard, because of a three-year differential between drinking ages in Connecticut (21) and nearby New York state (18). "Budd" writes: "...teenagers would run across the state line to drink...on returning it was littered with beer cans, wrecked cars and death, earning it its name."
One bit of trivia: some erased numbers on a 1931 state planning map hint at a more orderly set of numbers for routes in lower Fairfield County:
- Route 104 might have been Route 23
- Route 137 was penciled in (confirmed) as Route 27
- Route 29 would have fit as is
- leaving Route 123 as a possible Route 31
- Route 33 would have also fit as is
In the end, the state proceeded with matching neighboring states at the border, leading to the 104, 137, and 123 numbers assigned in 1932.