It passes through gently rolling farmland for ten miles (16 km) before entering the Des Moines River valley adjacent to Lacey-Keosauqua State Park.

The highway crosses the Des Moines River and enters Keosauqua along Main Street.

The next seven miles (11 km) run due north passing through Birmingham, before the highway crosses Cedar Creek south of Fairfield.

For the next nine miles (14 km), the highway continues due north through Jefferson and Keokuk County.

Iowa 1 passes through flat farmland before crossing the English River south of Kalona.

It curves to the north of Iowa City Municipal Airport, intersecting US 6 at Riverside Drive.

Iowa 1 continues north through Johnson County for twelve miles (19 km), passing through Solon.

At Solon, it intersects County Road F16, which provides access to Lake MacBride State Park.

On the northern edge of Mount Vernon, Iowa 1 crosses a major Union Pacific Railroad line.

three and a half miles (5.6 km) northeast of Martelle, Iowa 1 ends at a partial cloverleaf interchange with US 151.

[5] This section approximately follows part of the route of the territorial and military road from Dubuque to Iowa City.