Here's the paragraph from IL Publication 108 that explains why even though you've owned your home for years and it is your primary residence and you make less than $500k....etc. - that you may not get a property tax credit. This was applicable in my filing case because both in our house are retired and made so little taxable income in IL.
May I receive a refund if my property tax credit
exceeds the income tax I owe?
If your property tax credit exceeds the income tax you owe, you may
not receive a refund for that amount, and you may not carry unused
credit to other years. Your property tax credit may only reduce the
income tax you owe to zero.
