You must file Form IL-1040-X, along with proper supporting documentation, for both corrected and amended returns. To find out if you qualify, write a letter of request to the Illinois Department of Revenue, Sales.Note: The IRS and IL Department of Revenue (ILDOR) will send a separate letter with the amount of interest and penalties owed. All resident and nonresident aliens for tax purposes who earned income in the state of Illinois in 2023 must complete and file Illinois Form 1040. Find self-help tools to help you with your tax issues. Individuals who earned U.S.-based income must file additional documentation. No information is available for this page. The Illinois Department of Revenue sends letters and notices to request additional information and support for information you report on your tax return. I confirm that I am the taxpayer listed above. Sign up for Tax Refund Alerts. Email.