Thanks for the message. Your thoughts did give me pause. When I looked up common law marriage in Illinois, though, I came across this:
" Illinois was actually one of the earlier states to ban the practice—common law marriage in IL became outlawed in 1905. While couples who had entered into an existing common law marriage in Illinois still were considered married, no new common law marriages could be entered into in the state after this."
I think I need to keep looking. Thanks for your input!