Overview
Illinois employers subject to unemployment insurance must file quarterly wage and contribution reports with the Illinois Department of Employment Security (IDES). Separately, employers that withhold Illinois income tax must file Form IL-941 with the Illinois Department of Revenue.
The TaxBandits API supports automation of Form UI-3/40, Illinois's quarterly unemployment insurance contribution and wage report.
Forms supported
| Form | Type | Filing frequency | Due date |
|---|---|---|---|
| Form UI-3/40 | UI | Quarterly | Last day of the month following the quarter end |
| Form IL-941 | Withholding | Quarterly | Last day of the month following the quarter end |
Key compliance notes
- UI reporting. Employers subject to the Illinois Unemployment Insurance Act must file Form UI-3/40 quarterly and report employee wages and applicable UI contributions.
- Zero filing. Form UI-3/40 must be filed even when no wages were paid during the quarter, as long as the employer has not permanently ceased operations.
- 2026 UI wage base. Illinois UI contributions apply to the first $14,250 of wages per employee for 2026.
- Electronic filing. Employers with 25 or more employees during the prior calendar year are required to file their quarterly UI-3/40 reports electronically.
Filing due dates
| Quarter | Reporting period | UI-3/40 due date | IL-941 due date |
|---|---|---|---|
| Q1 | January – March | April 30, 2026 | April 30, 2026 |
| Q2 | April – June | July 31, 2026 | July 31, 2026 |
| Q3 | July – September | October 31, 2026 | November 2, 2026 |
| Q4 | October – December | January 31, 2027 | February 1, 2027 |
For Form UI-3/40, the standard due dates are April 30, July 31, October 31, and January 31.
API endpoints
Form UI-3/40
The TaxBandits API provides the following endpoints for Illinois UI reporting:
- Create — Creates a quarterly UI-3/40 contribution and wage report.
- Update — Updates an existing UI-3/40 report before transmission.
- Get — Retrieves the details of a previously created UI-3/40 report.
Common API operations**
The standard state filing workflow can be used for Illinois UI filings, including:
- List
- Transmit
- Status
- Request PDF URLs
- Delete
The StateFilings List endpoint supports Illinois (IL) and can filter state UI records by tax year, quarter, submission, filing status, and other criteria.
New hire reporting
Illinois employers are also subject to new-hire reporting requirements. New and rehired employees must be reported to the appropriate Illinois agency within the applicable reporting period.
All endpoints require an OAuth 2.0 access token. Call the Auth method and pass the token as a Bearer token in the request header.
Testing & notifications
The TaxBandits Sandbox can be used to test the Illinois UI-3/40 filing and validation workflow without transmitting actual returns to IDES. Webhooks can be configured to receive filing-status updates.