Where do i add my NYS real estate STAR credit?

If you paid a reduced property tax bill because the credit is applied to your bill (if you were enrolled in STAR before 2015), you don't need to do anything extra, your property tax bill is already reduced.  If you received a STAR rebate check, you must reduce the amount you report as a property tax deduction on the mortgage and property tax page in the Federal Deductions and Credits section.  You must do the calculation yourself.  For example, if your 1098 form shows you paid $3500 in property taxes, and you received a $300 rebate check, you should change the property tax to show $3200 (the full tax amount minus the rebate).