St. Peter's was dubbed “Mullen's Folly” when commissioned by Bishop Tobias Mullen in 1873. Its suburban setting and enormous size prompted sarcastic comments in the mostly rural, sparsely populated diocese. Mullen persisted in his choice of location, but refused to build until the funds were in hand, which delayed construction for twenty years. He prevailed and his funeral was held in St. Peter's in 1900.
The architect, Irish-born Patrick Charles Keely (often spelled Keeley), is documented as having designed 150 churches in the United States, but his obituary in American Architect in 1896 credits him with over 600 churches and 15 cathedrals ranging from Iowa to New York City and from New Orleans to New Brunswick, Canada. He began his architectural career in 1847 and practiced until 1890.
This cathedral has entrances at the base of each of its three towers. The central six-stage tower at 265 feet is the tallest structure in Erie and features small spires at the corners of its steeple. Enormous clock faces are on all of the tower's four sides. The smaller towers, also with steeples, that flank the central tower add to the building's impressive width. Windows and doors are lancet arched, and buttresses are capped with white limestone that contrasts with the building's golden-rose, rough-hewn, random-laid sandstone. Clere-story windows illuminate the marble and wood interior and highlight the vaults, which are supported on slender clustered columns that separate the nave from the aisles.