Long ago, Route 181 had a very short alternate route: Route 181A.
In the late 1920s, State Highway 181 followed today's Route 30 between Route 83 in Vernon and Route 74 in Tolland.
Today's Route 181, commissioned in 1932, was originally more of an east-west route, leading from Barkhamsted to Granby. Its original alignment:
When the Saville Dam and Barkhamsted Reservoir were created in 1940, the middle segment of Route 181 was submerged. At Day Road on the west bank, Route 181 was rerouted north along its modern alignment, ending at Route 20.
One of many bridges destroyed in the 1955 flood was a Route 181 bridge over Morgan Brook in Barkhamsted. The replacement bridge opened to one-way traffic on Nov. 30, 1956.