File Illinois Form IL-505-I
Prepare Illinois Form IL-505-I now with TaxAct
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Form IL-505-I must be filed only if a taxpayer did not file their tax return by the due date, if they owe a tentative tax, or if they are submitting their payment by money order or check. If an unpaid liability is found when the taxpayer is filing their tax return, the taxpayer may owe additional penalties and interest charges.