It is regarded as "one of the finest Prairie School buildings in the United States"[3] and has been declared a National Historic Landmark for its architecture.

It featured a mansard roof with iron cresting and a corner tower capped with a dome and a statue of Lady Justice.

The old courthouse was sold and the new one, designed by the Minneapolis architect George Grant Elmslie in collaboration with the Sioux City architect William L. Steele and Elmslie's partner, William Gray Purcell, was constructed from July 10, 1916 to March 1, 1918 at a cost of $850,000.

It is a nearly square four story structure, built out of Roman brick, with granite and terra cotta trim elements.

The interior floors are marble, and the central rotunda features a glass mosaic drinking fountain in one wall.