Construction began on October 27, 1887, and the money ran out before the roof was finished. Officials then discovered that federal loans were available for agricultural schools, so the building was renamed the School of Agriculture instead of the School of Mines.
Old Main opened for the first class on October 1, 1891. It held classrooms, a library, offices and dorms, and was the only building on campus. Six teachers taught 32 students.
The city condemned the building in 1938 because of neglect. The US Navy repaired it in 1942 for World War II, and it came back to campus use in 1945. A full renovation reopened it in 2014.