A competition was held for the projected state capitol building in 1869. Fourteen architects submitted designs, and from these, the design of Cochrane and Piquenard was selected. The Capitol Commission consulted Edward Clark, the Capitol Architect in Washington, D.C. He recommended that the best elevations were those provided by Piquenard but that the most satisfactory plans were by the Des Moines architect J. C. Farrand. The commission proceeded to appoint Cochrane and Piquenard as the architects for the Iowa State Capitol—and then gave the prize money to Farrand. Cochrane and Piquenard, who were then involved with supervising their winning design for the Illinois State Capitol, modified their Iowa plans and supervised the construction during its first years. With Piquenard's death in 1876, M. E. Bell, who had been in the Piquenard office, formed a partnership with the Des Moines architect W. F. Hackney, and they became the official architects for the Iowa State Capitol. Bell and Hackney modified the design for the drum and dome and also revised the interior. The interiors of the first floor and the legislative chambers were decorated by a consortium of artists that included Andreas Hansen, August Knorr, Fritz Melzer, E. S. Mirgoli, and several studios, those of Albert, Emeric, and McIvor; Noxon; and Toomey. After the turn of the century the interior decoration was brought to completion through the murals of Elmer Garnsey. Garnsey's work was joined by Edward Bashfield's Westward, a group of six mosaic panels over Frederick Dielman's grand staircase, and Kenyon Cox's series of eight lunette paintings within the rotunda.

The hilltop location of the capitol building is a splendid one. Ernest E. Clark, writing in 1895, noted, “It stands upon a commanding site, from which its golden dome can be seen for many miles. No Iowan who has a clean heart and wholesome State pride can catch a glimpse of that dome, when approaching the Capitol City, without a thrill of pleasure.” 16 Piquenard's final scheme for the building was directly inspired by the architect's recollection of L.-T.-J. Visconti and M.-H. Lefuel's mid-nineteenth-century design for the new Louvre in Paris. Its most Louvre-like quality is found in the four almost independent corner pavilions, each with its own small-scaled drum and dome. The building's plan was a traditional one: a central block organized around a rotunda that terminates in a dome, and then a cross axis on the ground floor and the first floor that penetrates through the two matched wings. The legislative chambers and the impressive law library are located on the second floor.

Much more than Cochrane and Piquenard's design for the Illinois State Capitol at Springfield, the Iowa State Capitol is an impressive summation of how the late nineteenth century viewed the classical tradition. Its forms and detailing are rich, and this was equally mirrored in the varieties of marble (29) and the many woods used inside. Instead of being a white shimmering pile on a hilltop, the Iowa capitol is a varied, warm-colored building that fits, at least symbolically, what the twentieth-century critic Lewis Mumford labeled, “The Brown Decades.” The exterior of the central dome of the capitol was first gilded in 1882, and was re-gilded in 1965. The building was extensively restored during 1983–1986 by Bussard Dikis, and improvements were made in the surrounding Capitol Mall (now some 165 acres) by Hansen Lind/ Meyer/Sasaki Dawson DeMay.