Route 175 was commissioned in 1932. The original route followed the current route to Route 176 and the current Route 176 and its former extension into Hartford along Newington Avenue. In 1940, the section north of the junction with Route 176 was transferred to Routes 176 and 176A. At the same time, Route 175 was extended east along former SR 775 to the Silas Deane Highway. In 1968, a section in Newington and Wethersfield was rerouted slightly to the north. Part of the old road was abandoned; the remainder was reassigned to modern SSR 405.