Illinois S corporation compliance calendar 2026: the filings and due dates

Each filing, in plain English

Owners' estimated tax payments

When: on April 15, June 15, September 15, January 15. Where: IRS (Form 1040-ES). If missed: An underpayment penalty computed on Form 2210, charged as interest on each short installment.

Income from an S corporation or a partnership is taxed on the owners' personal returns, and the IRS wants that tax paid during the year. Owners who expect to owe $1,000 or more pay in four installments: April 15, June 15, September 15 and January 15 of the following year. Withholding from a salary counts toward the total, which is why many S corporation owners cover it through their own paychecks instead.

Illinois harassment prevention training

When: by January 31 each year. Where: Illinois labor and civil rights agencies.

Illinois requires private employers to train employees on preventing sexual harassment. Every year, for all employees. The date here is a planning reminder at the start of the year; the legal timing runs from each employee's hire date and the last training.

Illinois unemployment insurance wage report

When: by the last day of the 1st month after each quarter. Where: Illinois unemployment insurance agency. If missed: Late filing and payment penalties set by the state, plus loss of the federal FUTA credit if contributions are not paid on time.

An employer registers for unemployment insurance in each state where it has employees and files a wage report every quarter, by the last day of the month after the quarter in nearly every state: April 30, July 31, October 31 and January 31. The contribution rate is set by the state each year. Paying on time also earns the 5.4% credit against the federal unemployment tax.

Illinois W-2 filing with the Department of Revenue

When: by January 31 each year. Where: Illinois Department of Revenue (Forms W-2 through MyTax Illinois).

Illinois dropped its annual withholding reconciliation in 2017. Employers file Form IL-941 every quarter, by the last day of the month after the quarter, and send the W-2 copies to the Department of Revenue electronically by January 31. A payroll provider does both.

Annual federal unemployment tax return

When: by January 31 each year. Where: IRS (Form 940). If missed: 5% of the unpaid tax for each month late, up to 25%.

Federal unemployment tax is an employer only tax of 6% on the first $7,000 paid to each employee, reduced to 0.6% for employers that pay state unemployment tax on time. Form 940 reports it once a year, by January 31. Quarterly deposits are due during the year once the liability passes $500. An organization exempt under section 501(c)(3) owes no federal unemployment tax and files no Form 940; other exempt organizations, such as 501(c)(4) and 501(c)(6) groups, do.

Quarterly federal payroll tax return

When: by the last day of the 1st month after each quarter. Where: IRS (Form 941). If missed: 5% of the unpaid tax for each month late, up to 25%, plus failure to deposit penalties of 2% to 15%.

Nearly every employer files Form 941 four times a year, by the last day of the month after each quarter: April 30, July 31, October 31 and January 31. It reconciles what was withheld from employees and what the employer owes in Social Security and Medicare tax against the deposits already made. The smallest employers, those the IRS has told to file Form 944 because their annual liability is $1,000 or less, file once a year by January 31 instead. A payroll provider normally files it; the company is still the one liable.

W-2 forms to employees and the SSA

When: by January 31 each year. Where: Social Security Administration (Forms W-2 and W-3). If missed: $60 to $340 per form depending on how late (the figures for forms due in 2026, adjusted yearly), with no cap for intentional disregard.

Employees need their W-2 to file their own taxes, so the deadline is early: January 31, both for the copy to the employee and the copy to the Social Security Administration. Penalties are per form and grow the longer the forms are late. Payroll providers prepare and file these as part of year end.

Illinois S corporation return

When: by the 15th day of the 3rd month after the fiscal year ends (March 15 for a calendar year). Where: Illinois Department of Revenue.

An S corporation doing business in Illinois files a state information return by the 15th day of the 3rd month after the fiscal year ends (March 15 for a calendar year), alongside the federal return, so the owners can report their shares on their own Illinois returns. Some states charge a minimum tax or filing fee with it; check the Illinois Department of Revenue page.

Federal S corporation return

When: by the 15th day of the 3rd month after the fiscal year ends (March 15 for a calendar year). Where: IRS (Form 1120-S). If missed: $255 per shareholder for each month late, up to 12 months (the 2026 figure, adjusted yearly).

An S corporation files Form 1120-S by the 15th day of the third month after its fiscal year ends, March 15 for a calendar year. The return itself owes no tax in most cases, but the late filing penalty is charged per shareholder per month, so a late return with three owners costs more than most people expect.