From the FAQs of the Ulysses S Grant Association:

Why were the papers transferred to Mississippi State University from Southern Illinois University - Carbondale?

The story of why the Grant Association Board of Directors made this decision is not available to the public since litigation was involved. We can say the papers coming to MSU resulted largely from the fact that MSU’s Giles Distinguished Professor of History, Dr. John F. Marszalek, was named to replace Dr. John Y. Simon, who passed away in 2008, as Executive Director and Managing Editor of the Grant Papers project. The determination of the Dean of Libraries and the MSU Administration created conditions that made it possible for the papers to come to MSU. The Association’s Board of Directors, led by Rhode Island Chief Justice (ret) Frank J. Williams, unanimously approved the transfer of the papers to MSU, which occurred in December 2008. The formal written agreement between the Association and MSU was signed on January 30, 2009.