Opened in 1907, McMillan Hall was the first, and for many years, the only women's dormitory on campus. The architects were the Philadelphia firm Cope & Stewardson, represented by James P. Jamieson. The general contractor was Bright Construction Company. With the coming of the first South 40 residence halls in the 1950s and early 1960s, McMillan Hall was remodeled to meet space needs for classes and departments, along with food service space for the campus community.
McMillan Hall is named for William P. McMillan and was given to the University by his widow, Eliza McMillan, as memorial to her husband. He was born in December 1841 in Canada. In 1867, he opened a wholesale hardware store, William McMillan & Company. He came to St. Louis in 1870 to establish the Missouri Car & Foundry Company, which was one of 18 companies to be merged into William K. Bixby's American Car & Foundry Company. McMillan became the Chairman of the Board of Directors. The McMillans gave $100,000 to Mary Institute, a college preparatory school formerly run by Washington University, to move out of its old, rundown building, and into a new building. Mrs. McMillan gave generously to the poor and unfortunate. When she died, among those included in her will were friends and family, as well as her household staff, to whom she gave "lifetime" salaries.