In the Upper Midwest, there were two branches of the King of Trails that converged at Sioux City, which then continued south to Council Bluffs.

In 1920, the Iowa State Highway Commission assigned route numbers to roads in order to improve wayfinding for travelers.

As sections of the Interstate Highway opened up between Council Bluffs and Sioux City, US 75 were rerouted onto the new road.

In the late 1990s and throughout the 2000s, the highway along with Iowa 60 were improved into a continuous four-lane expressway between Sioux City and Minnesota.

US 75 enters Iowa on the Sergeant Floyd Memorial Bridge, which also carries I-129 and US 20 from Nebraska, over the Missouri River.

The two routes split and US 75 continues to the north; it soon curves to the west around Bacon Creek Park.

In the northeastern corner of the city, two half interchanges complete the reconnection of the business loop to the mainline highway.

After crossing the western branch of the Floyd River, the four-lane, divided highway resumes.

On the western side, an interchange with Iowa 3 helps direct more traffic to the downtown area.

The last Le Mars interchange takes US 75 off of the four-lane road; Iowa 60 assumes the expressway.

Two miles (3.2 km) north of Maurice is an intersection with Iowa 10, which connects to Orange City and Alton to the east and Hawarden to the west.

A curve in the railway forces the highway to deviate from its due-north path, though it shortly resumes that course; the river again departs here.

It soon enters Rock Rapids and meets Iowa 9, the northernmost east–west highway in the state, west of the downtown area.

[3] US 75 was created in 1926 with the U.S. Highway System, but its route dates back to 1917 when the King of Trails Association formed.

The King of Trails entered Iowa at Council Bluffs and traveled north along the Missouri River to Sioux City, where it branched.

[6] In 1920, the Iowa State Highway Commission applied route numbers to the King of Trails — Primary Road No.

[9] As it was first planned out in July 1917, the road would connect 89 cities with populations over 1000 residents and nine military posts.

[10] Through Iowa, the King of Trails entered at Council Bluffs and traveled north along the Missouri River through Onawa and Salix before it reached Sioux City.

The western branch followed the Big Sioux River through the eastern tier of counties in South Dakota.

[11] There had been some competition between advocates for the South Dakota–Minnesota and Iowa–Minnesota routes, but in early 1918, compromise was reached and both forks were designated as the King of Trails.

[6] In 1919, the Iowa General Assembly passed a bill that created a fund for improving and hard-surfacing nearly 6,300 miles (10,100 km) of primary roads in the state.

Route numbers were painted onto telegraph and telephone poles in order to guide travelers without the need for maps.

12 from Council Bluffs to Sioux City, which included the western fork into South Dakota, and Primary Road No.

At Mondamin, the highway turned north again to run roughly parallel to the Missouri River.

Upon entering the city, US 75 followed Lakeport Road until reaching Morningside Avenue, which carried Iowa 141.

[16] North of Sioux City, US 75 followed a paved road that ran parallel to the Floyd River and two rail lines, the Chicago, St. Paul, Minneapolis and Omaha Railway and the Dubuque and Sioux City Railroad operated by Illinois Central.

When the 20-mile-long (32 km) section of I-29 opened between N. 16th Street in Council Bluffs and Missouri Valley, US 75 was rerouted off of its old Lincoln Highway alignment and onto the new freeway.

Within a few years, I-29 was complete between Council Bluffs and Sioux City and US 75 was shifted off of its two-lane road and onto the Interstate Highway.

Upon entering the state, northbound US 75 immediately exited onto southbound I-29 in order to reach Singing Hills Boulevard and resume its course.

[32] Part of the corridor improvements included two bypasses on US 75, the completion of the one around Sioux City and construction of one around Le Mars.