The architect of this church, Henry Martyn Conger of New York and Brooklyn, specialized in the design of religious buildings, especially for the Episcopal church. In style he moved between interpretations of the Gothic and the Richardsonian Romanesque. He designed numerous Episcopal churches in New England, New York, and on into the Midwest. At the time he was designing Saint John's in Dubuque he was working on similar churches in Portland, Connecticut, and in German-town, Pennsylvania. A few years earlier he had designed the Chapel of the Good Shepherd at Faribault, Minnesota (1873). His largest church in the Upper Midwest was Grace Church Cathedral at Topeka, Kansas (1889). The scheme of Saint John's Episcopal Church is pure nineteenth-century English Gothic Revival: cruciform in plan with rough limestone walls, smooth stone trim, and a large rose window at the front. The low, square tower, now crenellated, was meant to have a tall upper tower and spire, as in the work in England of Augustus Welby Pugin and others. Within the church are five windows from the studio of Louis Comfort Tiffany.