My fiancé and I moved in to a house together over 2 years ago. We chose the house together, but the mortgage is in his name only. I contribute significantly to the monthly household bills, but he feels that since I am not a "tenant", he can kick me out at will. What rights do I have? Does he have to follow Illinois eviction laws??

Yes you are a resident and he will have to evict you, including taking you to housing court. That is to evict you legally.
Now one day you may come home and the locks are changed, while not legal, this is common between boyfriend and girl friend, and normally the police will not get invovled but tell you to sue them.