St. Mary's is one of a dozen ethnic churches in the grid plan of Cambria City, a 10 × 4–block neighborhood of Johnstown on the opposite side of the Conemaugh River from Cambria Iron Company's Lower Works ( CA16). Settled a year after the company's founding in 1852 by Irish and German workers, the neighborhood of modest row houses and single-family residences is dotted with spires and domes from a remarkable group of churches. Pittsburgh-based John Comes designed this Byzantine-derived Catholic church for its Carpatho-Rusyn, or eastern Slavic, congregants. The building is cruciform in plan, with a multicolored dome at the crossing that is echoed by two similarly colorful domed towers at the corners of the facade. Glazed brick, foliated stonework, and richly colored mosaics and tiles at the door surrounds further enliven the building's mottled brick of yellow, brown, and tan. The interior has round-arched vaults and a central aisle.
Ten years earlier, in 1913, Comes designed St. Columba's for a largely Irish congregation (918 Broad Street). The chocolate-brown brick, tile roof, and limestone trim are configured in what Comes called his “Lombard Romanesque” style: a gable-roofed facade with a single tower to the west, and elaborate corbeling at the roofline and in the gable end.