I just came across the same issue. There is an error in TurboTax. My Illinois return shows a preperty tax credit of zero. On schedule ICR, which is used to compute the credit, the credit is properly computed on line 4g. Then on line 5 it says to take the lesser of line 4g and line 3 (tax due before nonrefundable credits). The amount TurboTax put in there is zero. Clearly an error. I suggest you fill out your own Illinois form, if you have not already filed, put the correct amount in line 5 (most likely the amount from line 4g). Adjust line 6 of schedule ICR and follow the changes onto the IL-1040 so you can take the credit. It is near the end of the return, so there will not be that many lines to change.
If you have filed without taking the credit, you should be able to file an amended return.
I have been doing my state return for years (this is the first year using TurboTax) and that is definitely an error. As long as you have tax due you can take the credit. (It is nonrefundable, so the credit is limited to the tax due before the credit.)
I can't find any way to contact TurboTax to report this error, but hopefully someone monitors this board.
