The John K. Mullen of Denver Library was built in the 1920s, but the University needed a library long before its construction. In 1901 CUA’s second Rector, Thomas Conaty, was well aware that the University needed a separate library building.  The University had been receiving collections of manuscripts and books since it had opened in 1889. These collections had moved from Caldwell Hall to McMahon Hall, but clearly there was a space problem.

Thomas Shahan, who played a critical role in raising money to build the Shrine, also instigated the fundraising for a university library.

The library’s namesake John Kernan Mullen of Denver, Colorado, a Milling and Elevator Company magnate, donated $400,000 to CUA for the construction of a library. In fact, there were complications attached to this gift, and the library actually had to be completed in phases: the full basement and front and central portions of the library were completed and opened in 1928, while the side portions were completed in 1958.