735 ILCS 5/6-122: Action against co-tenants.

If the action is brought by one or more tenants in common, or joint tenants against their co-tenants, the plaintiff, in addition to all other evidence which he or she may be bound to introduce, shall be required to prove, on the trial of the cause, that the defendant actually ousted the plaintiff, or did some other act amounting to a total denial of his or her right as such co-tenant.