The Gannon campus covers approximately twelve blocks of central Erie and consists of nearly thirty buildings. Many of the structures are office blocks and apartment houses converted to student and classroom use, the most interesting of which is the forty-six-room Scott-Strong house (1896; 109 W. 6th Street) by Green and Wicks, a Buffalo firm. Anna W. Scott Strong, heir to the fortune of her father, William L. Scott, and wife of the wealthy Charles H. Strong, presided over Erie's social and cultural life from the 1890s until her death in 1928. The house her father commissioned and gave to her was a fitting setting for her activities and perhaps indicative of Strong's social aspirations. Its soaring hipped roof is pierced by gables and gabled dormers. Although often labeled Richardsonian Romanesque because the first story is stone and has a triple-arched entrance, the house is actually closer to the Chateauesque style that Richard Morris Hunt popularized in New York City.
Adapting some apartment buildings and single-family homes to living spaces for students and faculty, the school grew from this single mansion into fifteen nearby buildings by 1956. Wehrle Hall and a Student Union were built in the 1950s. Four more buildings, acquired and built in the 1960s, are basically brick rectangles with flat roofs. In the 1970s, the college commissioned Zurn Science Center (Goldberg and Heidt Architects; 143 W. 7th Street) and two buildings by Heidt-Evans Partnership: Finnegan Hall (1972) at 120 W. 5th Street and Nash Library (1974) at 619 Sassafras Street. In 1999, the John E. Waldron Campus Center by WTW architects (124 W. 7th Street) integrated several older buildings behind a new eclectic red brick facade with gabled-, pyramidal-, and mansard-roofed sections facing the campus green. The Carneval Athletic Pavillion by Rectenwald Buehler, Architects (c. 2004; 130 W. 4th Street) provides students with a pool, gymnasium, and racquetball courts.
Between 1989 and 1993, Villa Maria Academy, by then a women's college, was absorbed by Gannon. Its former campus at 819 W. 8th Street included an 1892 motherhouse for the Sisters of St. Joseph designed by David K. Dean and Sons, with a large addition in 1904