According to the University, there were sellouts in both seasons.
http://fightingillini.com/sports/2016/8/18/football-attendance-records.aspx
Yea I see what you were saying. That is most likely tickets sold, not actual crowds (just like I don’t remember the NC game in 2016 being sold out). The OSU game in 2011 stands out to me because of all the hype (beat RG3 in the bow l game the year before, won the first 6 games) and we still were about 4-5000 short of a sellout. It takes sustained success for a couple years to bring the fans back, especially Illinois ones.