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The Illinois law in question states in part:
770 ILCS 60/1(a)
Any person who shall by any contract or contracts [...] with the owner of a lot or tract of land [...] improve the lot or tract of land or for the purpose of improving the tract of land [...] has a lien upon the whole of such lot or tract of land [...].
In other words, the contractor automatically has a lien on your property once he improves the property. Accordingly, even if the work isn't finished, he has a lien if the property was improved. On the other hand, if the work is so unfinished such that there is no improvement, then the contractor would not yet have a lien.
However, assuming he has a lien because the property was improved, then he would still need to perfect the lien by filing a notice in the office of the recorder of the county. This notice must be filed and enforced within 4 months of completion of the work, or the lien expires automatically.
Does that answer your question? Please let me know if you need clarification, as I am happy to continue helping you until you are satisfied.