Going by current conference lineups, the Big Ten and the SEC are by far the most popular and both are set to get 4m+ more fans with realignment. Both the Big 12 and PAC 12 are set to fall below 10m. Ohio State is #1, Alabama #2, Penn State #3. One wonders how long Notre Dame can hold out:
Big Ten (26.6m): OSU (6.3m), PSU (4.0), MSU (2.9m), UM (2.9m), Illinois (1.7m), Wisconsin (1.6m), Minnesota (1.4m), Iowa (1.3m), Nebraska (1.2m), Maryland (.9m), Indiana (.8m), Purdue (.6m), Rutgers (.6m), Northwestern (.4m)
SEC (21.4m) : Alabama (4.1m), Georgia (2.8m), LSU (2.3m), Florida (2.1m), Auburn (2.0m), Texas A&M (2.0m), Kentucky (1.5m), Tennessee (1.3m), Missouri (1.1m), Arkansas (1.1m), Miss State (.5m), South Carolina (.4m), Mississippi (.1m), Vanderbilt (.1m)
Big 12 (10.1m): Texas (3.1m), Oklahoma (1.7m), Kansas (1.0m), WVU (.8m), Baylor (.8m), OSU (.8m), KSU (.7m), Iowa State (.7m), TT (.3m), TCU (.2m)
ACC (16.4m): FSU (2.8m), Duke (2.6m), UNC (1.9m), Boston College (1.5m), Georgia Tech (1.5m), Clemson (1.5m), Miami (1.1m), Syracuse (.9m), NC State (.7m), UVA (.6m), Pitt (.5m), Virginia Tech (.4m), Louisville (.3m), Wake Forest (.1m)
PAC 12 (11.8m): UCLA (2.7m), Arizona State (1.5m), USC (1.5m), Oregon (1.0m), Stanford (1.0m), Washington (.8m), Arizona (.8m), California (.8m), Oregon State (.7m), Utah (.4m), Washington State (.3m), Colorado (.3m)
Notre Dame 3.5m
Big Ten (26.6m): OSU (6.3m), PSU (4.0), MSU (2.9m), UM (2.9m), Illinois (1.7m), Wisconsin (1.6m), Minnesota (1.4m), Iowa (1.3m), Nebraska (1.2m), Maryland (.9m), Indiana (.8m), Purdue (.6m), Rutgers (.6m), Northwestern (.4m)
SEC (21.4m) : Alabama (4.1m), Georgia (2.8m), LSU (2.3m), Florida (2.1m), Auburn (2.0m), Texas A&M (2.0m), Kentucky (1.5m), Tennessee (1.3m), Missouri (1.1m), Arkansas (1.1m), Miss State (.5m), South Carolina (.4m), Mississippi (.1m), Vanderbilt (.1m)
Big 12 (10.1m): Texas (3.1m), Oklahoma (1.7m), Kansas (1.0m), WVU (.8m), Baylor (.8m), OSU (.8m), KSU (.7m), Iowa State (.7m), TT (.3m), TCU (.2m)
ACC (16.4m): FSU (2.8m), Duke (2.6m), UNC (1.9m), Boston College (1.5m), Georgia Tech (1.5m), Clemson (1.5m), Miami (1.1m), Syracuse (.9m), NC State (.7m), UVA (.6m), Pitt (.5m), Virginia Tech (.4m), Louisville (.3m), Wake Forest (.1m)
PAC 12 (11.8m): UCLA (2.7m), Arizona State (1.5m), USC (1.5m), Oregon (1.0m), Stanford (1.0m), Washington (.8m), Arizona (.8m), California (.8m), Oregon State (.7m), Utah (.4m), Washington State (.3m), Colorado (.3m)
Notre Dame 3.5m