The seven-story South Building of the Department of Agriculture, with its 4,500 office bays, was envisioned as a functional annex to the main departmental building on the Mall. Two arched bridges at the third-floor level over Independence Avenue link the buildings, which together suggest the importance of agriculture to the country.

The elevations of the South Building on 12th and 14th streets were to be visible from the Mall. The 14th Street side is sheathed in limestone, with a central entrance pavilion composed of sixteen monumental Corinthian columns. The 12th Street side is also of limestone. The two long elevations are clad in variegated tan brick and terracotta trim.

Interior lightwells along the C Street side provide natural illumination to the huge building. The spandrels between windows are ornamented with relief panels depicting animals native to the United States, among them turkeys, eagles, horses, bulls, and rams. The animal motif is carried out in the medallions in the frieze on the 14th Street side. All are the work of sculptor Edwin Morris. Pilasters articulate the large wall masses and separate windows of varying widths. Terracotta fretwork and strips at the water table and parapet further adorn this massive structure.