In the 1920s, State Highway 122 followed today's Route 25 between US 1 and US 6.

The modern route 122 dates back to 1932. The original route was 8.87 miles long:

• today's Route 162, from US 1 in Milford to Ocean Ave. in West Haven
• Ocean Ave. (now SR 705) to Beach St.
• Beach St. to First Ave. Part of Beach St (and part of former Route 122) is now closed to traffic.
• First Ave. to Campbell Ave. (former Route 158)

In 1951, Route 158 was deleted, and Route 122 was extended north, taking over most of Route 158, to Route 63, where its north end is today.

In 1967, Routes 162 and 122 were changed. The south end of Route 122 was truncated to I-95 at SR 745 (First Ave.) Route 162 was extended about 5 miles southwest along former Route 122 to US 1.

Route 122 relocation at Savin Rock

In the early 1960s, a redevelopment plan for the Savin Rock area included relocating Route 122 a couple blocks inland from Beach St. In 1962, the City of West Haven Planning and Zoning Committee announced a comprehensive street plan for the city. This plan recommended that the relocated Route 122 be four lanes wide.

The plan recommended relocating Route 122 between Ocean Ave. and First Ave. This was not completed; but a new late 1980s project harks back to that plan: Capt. Thomas Blvd., a four-lane divided road opened, and a segment of Beach St. was closed. However, Route 122 had already been moved from the area in 1967.