Electronic filing mandate

Any taxpayer required to file its federal income tax return electronically is required to file its equivalent Illinois income tax return for the same taxable year electronically, per Title 86, Part 760, Section 760.100(c)(4). This subsection (c)(4) does not require you to electronically file amended returns, returns of individuals or estates, or any return the Department has announced you cannot electronically file.

Returns supported for electronic filing

You can electronically file the following return types:

• C Corporation
• S Corporation
• Estimates
• Extension
• Consolidated / Combined*
• Short year (ending after December 26)
• Unitary (with no passthrough members)

*Combined returns with all C Corporation members can electronically file if Illinois is attached to all members.

For a comprehensive list of forms and schedules that are included in the electronic file, see Forms included in the electronic file.

Returns not supported for electronic filing

You cannot electronically file the following return types:

• Amended returns
• Returns with late interest, failure to file penalty, and failure to pay penalty
• Unitary returns with Partnership or S Corporation members
• Power of Attorney
• Foreign corporations
• Annual report

Signature requirements for electronic filing

Illinois does not have a specific signature form for corporate returns. Instead, Illinois considers the signature date you enter on Screen ILELF and the act of completing and filing electronically an authorized signature.

Resubmitting returns

If you need to make a change to a return that you have already electronically filed, and Illinois has already accepted it, you must amend and paper file the return.

If Illinois rejects a Business Income Tax return filed timely through MeF, you must resubmit and have Illinois accept the return within 10 calendar days after you initially received the rejected acknowledgement to avoid penalties. Perfection for electronic retransmission is generally required when the original return had errors in the XML format or errors that caused that return to fail Illinois e-file schema validation or business rules.

Attachments

Illinois requires a valid federal attachment in the electronic file. Therefore, if the federal return is not supported for electronic filing by the IRS, you cannot e-file the state return. See 1120-US: Forms that are not eligible for electronic filing for a detailed list. 

Illinois does not support PDF attachments in the electronic file.

Payment methods

The Illinois DOR accepts direct debit (EFW), electronic funds transfer (EFT) or paper check/money order for balance due returns and estimates. If you file an extension electronically, you must pay via Electronic Funds Withdrawal (EFW).