It has a western terminus at Nebraska Highway 50 south of Syracuse and an eastern terminus at U.S. Highway 75 south of Nebraska City.

N-128 begins at an intersection with N-50 south of Syracuse and heads east through farmland.

Just west of Lorton, it meets Nebraska Highway 67.

They run concurrent through Lorton, and separate east of there.

N-128 continues east through the unincorporated community of Paul and ends shortly afterward at US 75.