Illinois State Tax Deadline 2025. This free webinar provides information about form changes for individual income tax, business income tax, withholding income tax, and sales tax. The deadline for most people to file their 2024 federal tax return is april 15, 2025.

The deadline for most people to file their 2024 federal tax return is april 15, 2025. Startup companies based in chicago have several important tax deadlines in 2025, including the april 15th federal and illinois tax return filings (which can be extended until october 15th).