The oldest of the remaining churches built in the area affectionately known as "Piety Hill," St. Paul's moved to its present building in 1885. Designed by Foster and Liebbe, Architects, of Des Moines, the building was essentially a one-story masonry Gothic church and basement with a bell tower topped by a wood-framed steeple – a style that could be called English Rural Gothic.
The surroundings have changed considerably since then. Ninth and High Streets have been substantially lowered so that the rough stone basement once buried in the hill is now visible in the present courtyard. In 1939, a kitchen was added under the Sanctuary. The crypt, now known as the Undercroft, was the Sunday school area, with curtains dividing the classrooms. The rooms on the south side housed the church office and the Rector's office and study. The small chapel on the east side is now used as a storage room. A coat hall and stairwell in the northwest corner of the building served as one of the exits from the nave; most of that area now houses the main organ blower.
The wooden steeple, which toppled during a storm in the 1930s, was eventually replaced in the 1960s by a new steeple in a skeletal form of the original, but built of Cor Ten steel. This structure was later removed, and the tower top strengthened to receive the carillon.
The parish house, designed by Proudfoot Bird and Rawson, and Brooks Borg Architects, of Des Moines, was added in 1952. The new addition created space for Sunday school classrooms, relocated clergy and staff offices, the Guild Hall, and the current chapel.
In the 1940s, the chancel was redecorated according to a scheme by the Rambush Company. When the high reredos (a decorative screen) was installed with the altar attached, three of the stained glass windows in the apse had to be removed and later relocated to the south wall of the narthex. The sanctuary and apse were repainted; with the apse ceiling painted blue with gold stars and fleurs-de-lis. Later the apse was painted gold as it is today. A ramp was added in the narthex, more to aid the transport of caskets than as a precursor to the American Disabilities Act.
At some point, the altar was detached from the reredos and moved south so the celebrant could face the congregation. Much restoration has been needed over the years, partly because of vandalism. A bomb blast at the Des Moines Chamber of Commerce building resulted in the destruction of the rose window and the other stained glass windows along the south wall of the nave and narthex.
In the 1980s, when the building was showing signs of age, the Vestry made a conscious decision to remain downtown; the congregation undertook a $1.4 million renovation the Second Century Restoration – under the direction of Des Moines architect William Dikis. When the new organ was installed in 1993, the wall-to-wall carpet was removed, along with the pews. New floor sheathing was installed, followed by slate-pattern vinyl tile, with only the aisles and crossovers carpeted – a change that made the music of the new organ come alive. The chancel area was remodeled, extending south toward the nave. Risers were built for the choir, and the pulpit and lectern were moved forward. The new organ console sits in its own recessed area. The St. Sacrament Chapel was built and installed on the east wall, reusing the original tabernacle from the north altar.