Note: For tax years beginning on or after January 1, 2017, the Illinois Property Tax Credit is not allowed if the taxpayer’s adjusted gross income for the taxable year exceeds $500,000 for returns with a federal filing status of married filing jointly, or $250,000 for all other returns. It's all or nothing line 1 of Illinois 1040 $500,000 (MFJ), you get it; $500,001 you get nothing.
see ILL PUB 108
https://tax.illinois.gov/research/publications/pubs/illinois-property-tax-credit.html
