Illinois Tax Deadlines: Individual & Corporate Filing Guide

Illinois Tax Deadlines: Individual & Corporate Filing Guide

Check Illinois tax deadlines for individuals and C Corporations. Confirm due dates, extension rules, and exemptions for S Corps and Partnerships.

Illinois uses separate forms and deadlines from federal returns.

Illinois Tax Deadlines at a Glance (2026)

Entity Type

Return Due

Extension Deadline

Individuals

April 15, 2026

October 15, 2026

C Corporations

April 15, 2026

October 15, 2026

S Corporations

March 16, 2026

September 15, 2026

Partnerships

March 16, 2026

September 15, 2026

Businesses

Replacement tax applies to corporations, S corporations, and partnerships.

Composite Returns

Available for nonresident owners.

‹ Indiana Tax Deadlines: Individual & Corporate Filing Guide

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Customer Stories

Trusted by firms across the board

"Research used to be a black hole. Now, I just type the question and get a citable IRS answer in seconds."

Tax Manager

Sama Tributa

"80% faster first drafts. What used to take us two days is now done in two hours."

Managing Partner

Northbridge Tax Advisory

Customer Stories

Trusted by firms across the board

"Research used to be a black hole. Now, I just type the question and get a citable IRS answer in seconds."

Tax Manager

Sama Tributa

"80% faster first drafts. What used to take us two days is now done in two hours."

Managing Partner

Northbridge Tax Advisory