Tell your landlord that you spoke to an attorney, and that you were told that because the lease specifies that the rent payments be sent to a PO Box, it was considered to be paid when the check was mailed.thank you much for all the answers to this question.
the lease says 'rent is to be paid to:<name> P.O.Box <number>" etc...since i do not know how to hand deliver to a p o box i think it is implicite that it should be mailed.
Although, i am under the impression she will pick up cash, she picks up cash in her own time and charges for that time....5 dollars a day.
Then hand her the case law that I quoted above, and tell her that the attorney was confident that Illinois courts would rule the same way that Oklahoma, Texas, and California courts did in similar circumstances.
Let us know what the landlord says.