Chemical Laboratory / Oliver Albert Harker Hall
Built in 1878, Harker Hall was designed by Nathan Ricker and John M. Van Odsel  to be the new Chemical Laboratory for a cost of $45,000 . The 23,700  square foot building is the oldest continually occupied building and the oldest classroom building on campus. Only Mumford House precedes it as the oldest campus building still extant. The Board of Trustees elected to rename the building on September 26, 1941 for Judge Oliver A. Harker,  who served as the first University council and as the third dean of the School of Law from 1903 to 1916. 
"Represent[ing] his philosophy of combing historical reference with current technical advancements", Harker Hall was Ricker's first major building construction. Its Second Empire Style was dictated by the Board of Trustees to match the neighboring New Main Building. The design featured an English basement and I-shaped Italianate style. The building's exterior used "course rubbled" Kankakee limestone, with reddish brown brick and "Joliet limestone trim" for the upper floors. The mansard roof was black slate with red and green shingles interspersed. 
Ricker worked closely with Professor Weber of the Chemistry Department to make the laboratory the premier chemistry laboratory in the nation. He employed his own students as draftsmen and made proficient use of the Architecture Department's woodshop for the building's furnishings. 
Harker also served for a short time as the home of the Mechanical Engineering Laboratory. From 1893 to 1895, two rooms in the basement housed "engines, boilers, pumps, condensers, indicators, gauges, scales, dynamometers, and various other devices necessary for practice in mechanical engineering". 
A lighting strike on August 16, 1896  badly burned the top story of the building and its original mansard roof. James M. White, a colleague of Ricker's from the Architecture Department, was charged with repairs and replaced the roof with a "hip roof supported by wood trusses with metal tension rods",  totally $40,000. 
By 1902, the Department of Chemistry had outgrown the building and the School of Law moved in, converting the building to classroom space and a library until they moved to Altgeld in 1927. James M. White was brought in to lead the renovation, which cost $8,000.  In 1926, James White and Charles Platt remodeled the building for the Department of Entomology.  In 1930 the Department of Botany moved into a portion of the second floor, while the ground floor and a single room of the second floor were converted into classrooms.  By 1970, the building had fallen into disrepair and campus planners recommended that it be torn down. 
In 1986 the building was listed on the National Register of Historic Places  and in 1992 it became the first permanent home of the University of Illinois Foundation, after gifts from Maybelle Leland Swanlund and former Foundation director William G. Karnes funded the renovation and restoration of the structure. The exterior was restored to its original condition, but the interior was gutted and refurnished.  The $3.5M contributed by Swanlund was also used to construct the Swanlund Plaza, which fronts the building on its southern side, looking onto the Quad.