You can take, as a subtraction against Illinois income, the portion of the $1,000 that relates to the portion of your investment that was exempt from federal tax, but taxable by Illinois.
If your entire portfolio is the federally tax-exempt income, you can claim the entire expense. If, say, 25% of the portfolio is reflected by this income, you can claim 25%. Make a reasonable estimate.
See Schedule M IL-1040 Instructions for more information.
