Sole Proprietorship Tax Deadlines in Illinois
Federal and state filing dates, extensions, and estimate schedules for 2026.
Illinois filing deadline
Business income reported on IL-1040.
Due: Apr 15, 2026
Extension: Oct 15, 2026
Form: Form IL-1040
Estimated payments
Estimated payment dates: Apr 15, 2026, Jun 15, 2026, Sep 15, 2026, Jan 15, 2027.
Due: Apr 15, 2026
FAQ
Does Illinois require Sole Proprietorship estimated payments?
Estimated payments are scheduled for Apr 15, 2026, Jun 15, 2026, Sep 15, 2026, Jan 15, 2027.
Where can I file Illinois Sole Proprietorship taxes?
Use Illinois Department of Revenue resources at https://tax.illinois.gov for forms and filing instructions.