Per the instructions for Form CT-1040 the maximum credit is $300. It is figured on Schedule 3 of your Form Ct-1040. There is a reduction in the credit, according to the Connecticut State Department of Revenue website, it states as follows:
"Depending on the amount of property taxes paid by you to a Connecticut municipality and your Connecticut adjusted gross income, the amount of your property tax credit may be reduced or you may not be entitled to a credit".
I have provided a link to the instructions below.
This table is in the instructions for Schedule 3, which is the Schedule that determines your property tax credit:
Click here for Instructions to CT-1040; See page 14 of this instruction under Schedule 3.