So far, following counties are known to allow prepayments:
Cook, DuPage, Grundy, Kane, LaSalle and Will.
Cook first installment only; can be paid online – bills already available online. Also by mail (postmarked by 12/31/2017) or at any Chase Bank branch in Illinois.
DuPage and Grundy can be paid in person or by mail (postmarked by 12/31/2017)
Grundy up to 100% of amount paid in 2017 taxes for 2016 taxes.
DuPage up to 105% of amount paid in 2017 for 2016 taxes.
Kane can be paid in person or by mail, but it must be RECEIVED by 4:00 PM on 12/29/2017 even if by mail.
Kane up to 100% of amount paid in 2017 taxes for 2016 taxes rounded down to the nearest $100. Also must use the Application for Kane County Property Tax Prepayment Program form available online.
LaSalle and Will county in person only by 12/29/2017. Up to 100% of amount paid in 2017 for 2016 taxes.
Kendall County is not allowing prepayment.