St. John's is one of a handful of churches in the United States with a full set of Tiffany windows and a Tiffany mosaic. Installed between 1901 and 1917, the windows depict the four Evangelists, Sts. Agnes and Michael, and Christ. Two additional mosaics by the Gorham Art Glass Studios of New York illustrate the Nativity and the Resurrection. The large rose window in the facade is gold and rose in color. Rosewood pews and marble floors complete the colorful ensemble. The square tower attached to the facade of this Gothic Revival church has diminutive turrets at the corners of its pyramidal roof. A wood-lined chapel, with oak hand-carved pews and benches and German stained glass, was added at the rear in 1965. The stone-veneered parish house to the south predates the church, as does the frame Queen Anne rectory at the southwest corner of 12th and Buffalo streets.
This block of Buffalo Street has two more churches: the tan brick Christ United Methodist Church (c. 1950; 1135 Buffalo Street), and the white frame Faith Holiness Church (1887; 1101 Buffalo Street). The latter, built for a German Lutheran congregation, has a square bell tower embellished with sawn ornament and Stick Style trim on its various wooden surfaces.