For much of 2018, speculation involving further league expansion focused on Augustana University, a Division II school located in the Summit's headquarters city of Sioux Falls. Many of the school's boosters have ties to Sanford Health, a hospital company that has long been a major league sponsor and also owns the office complex that houses the league headquarters. The university announced on December 14 that it would start a transition to Division I, though stating at the time that no such move would take place until at least 2021. The conference expanded anyway, announcing in June 2019 that UMKC would return in 2020 after a seven-year absence. However, shortly thereafter, Purdue Fort Wayne announced its 2020 departure for the Horizon League, maintaining the full-time conference membership at nine schools. Then, on October 4, 2019, the University of St. Thomas, a Minnesota school that was set to be expelled from its longtime athletic home of the NCAA Division III Minnesota Intercollegiate Athletic Conference (MIAC) in 2021, announced that it received an invitation to join the Summit upon its MIAC departure. St. Thomas eventually received a waiver of an NCAA rule mandating that Division III schools can only transition to Division II, allowing the school to move directly to D-I on the originally announced schedule.