Although it depends on the bank (sadly most banks are not very well organized at this), but generally the bank should accept your payments so that you can cure your default. In the even they don’t, you have a statutory right to reinstate your mortgage should the lender initiate a foreclosure action. You might want to call your lender and find out what is the best way to make a payment. Good Luck.
As the other attorney said, hopefully. Thankfully, if the bank doesn’t accept payment for any reason, you can exercise your right to reinstate, but in Illinois that period when you have a right to reinstate (pay back the entire amount due plus fees and costs) begins when you are served with a summons for foreclosure and extends for 90 days thereafter. So, if you haven't been served with foreclosure papers yet, it is a slightly different story. Basically you will have to work with the bank. If you have difficulty, you can hire an attorney to help you. Otherwise, I would also suggest looking closely at your default notice or any notice that you receive from the bank in the mail. According to your mortgage terms (usually set out in paragraph 22 of your mortgage) the bank must send an acceleration notice prior to filing foreclosure telling you the exact amount that you owe and granting you thirty days to pay that amount. According the terms of you mortgage, the bank is supposed to send you that letter giving you the opportunity to satisfy the default within 30 days before accelerating the loan and filing foreclosure. In fact if the bank does not send this notice prior to filing foreclosure it is grounds for dismissal for failure to satisfy a condition precedent.
The information in this answer is not intended as legal advice nor do I intend to create an attorney-client relationship with any reader simply by answering this question or contributing as a member of AVVO.