St. Augustine Church is one of at least 20 church buildings in the upper Mississippi River valley designed and erected under the supervision of Father Samuel Mazzuchelli, a Dominican missionary and amateur architect. Father Mazzuchelli was born in Milan, Italy in 1806 and came to the United States at age 22. His original missionary work focused on the Green Bay area, but in 1835 he transferred his efforts to the lead mining areas of the Upper Midwest. In Wisconsin he founded congregations in Prairie du Chien, Potosi, Schullsburg, and New Diggings.

The church he built in New Diggings displays Fr. Mazzuchelli's personal interest in architecture. St. Augustine is a small, wooden building with a belfry tower above the entrance. At first glance, the building appears to be an example of the Greek Revival style, but closer inspection reveals other stylistic elements and displays Mazzuchelli's loose interpretation of architectural ornamentation. A projecting cornice accented with dentils caps the building. The frieze of the side elevations wraps around to the end gables in a typically modest interpretation of the Greek Revival style. However, this frieze is decorated with a fanciful Greek key motif. The corner pilasters have indented panels with a pointed arch. This picks up the Gothic motif of the front entry and the side windows, both of which have pointed arches and implied tracery. The tracery is all of wood, as is the entire sheathing of the building. The boards are incised to resemble masonry blocks. The belfry is ornamented in the same manner as the main part of the building, but with the decorative elements in a proportionally smaller scale. Mazzuchelli's unorthodox use of decorative features creates a highly original interpretation that combines two popular ecclesiastical styles of the period.

Located at the back of the building is a small extension that served as the priest's occasional home when he was not out on his ministry circuit.

The building is not regularly open to the public, please respect the rights of its owners.