Prior to December 1999, the road currently designated as Iowa 122 was a segment of
U.S. Highway 18. In that year, the state completed work on a new
freeway segment of US 18, bypassing Mason City to the south. This bypass was part of the
Avenue of the Saints project. The bypassed segment of US 18 was designated as Iowa Highway 122. Iowa 122 originally incorporated all of the bypassed segment of US 18. Its original eastern end was at
Rudd, at the junction with Floyd County Road T26. In 2000, a new segment of Iowa 122 opened east of Rudd, connecting 122 with 18 directly. In 2001, the segment between
Nora Springs and Rudd was turned over to
Floyd County. In 2003, the segment between Mason City and Nora Springs was turned over to
Cerro Gordo County. ==Major intersections==