McMillen Lab was begun in 1968 and completed in 1969. It is home to the Department of Chemistry in Arts & Sciences. Joining McMillen Lab to Bryan Hall is Millstone Lounge.
The building is named for George F. McMillen who was born and schooled in Kansas. He served as an executive for Ralston Purina Company for 25 years until he retired. He was a member of the advisory board for the Salvation Army and was a member of the Missouri Athletic Club and Bellerive Country Club. Among his gifts to the Salvation Army were a pool and bath house for the Army's Camp Mihaska at Bourbon, Missouri. He also had an active interest in the education of youth, and careers in natural and physical sciences, as well as engineering. He gave $100,000 to Washington University's Department of Student Aid to establish the George F. McMillen Student Loan Fund, and $1 million to build a new chemistry building in 1967, McMillen Lab.