It was designated in 1936 to connect Pikes Peak State Park to the primary highway system, which it did until it was turned over to Clayton County in 2003.

It was turned over along with 700 miles (1,100 km) of other short highways that primarily served local traffic.

Aside from a short connector to the state park gate, the route was a part of the Great River Road.

Iowa 340 began at the gate entrance to Pikes Peak State Park south of McGregor.

Now heading north, Iowa 340 took a series of curves and descended 300 feet (91 m) in elevation into the Mississippi River valley in which McGregor is nestled.