The Sun Prairie Downtown Historic District is a historic streetscape of nineteenth and early twentieth century commercial buildings lining both sides of the 100 and 200 blocks of East Main Street (State Highway 19); these buildings constitute the historic business center of Sun Prairie. The buildings in the district are very good brick-clad examples of the Queen Anne, Romanesque Revival, Neoclassical Revival, Twentieth Century Commercial, Georgian Revival and Contemporary styles and of the Commercial Vernacular form. Several of them are also fine examples of the work of important Madison and Ripon architects.

Among the most notable of these buildings are the Romanesque Revival style former Sun Prairie City Hall, built in 1895, and the Georgian Revival style former Sun Prairie Public Library, built in 1924, which is now the home of the municipally owned Sun Prairie Historical Museum and Library. Collectively, these buildings have a significance that is even greater than the merit they possess individually. These buildings are not only the most intact group of surviving historic buildings in Sun Prairie that were associated with that community's historic retail stores and other service-oriented commercial enterprises; they also comprise a large percentage of all the buildings that were ever associated with the city's commercial history through the end of World War II.