Illinois Business Taxes: Registration, Forms & Filing Guide

The four agencies that govern Illinois business taxes

Running a small business in Illinois means dealing with four separate government bodies. Each agency handles a distinct piece of your compliance, from legal entity standing to payroll and income taxes.

Knowing which department manages which form keeps you from sending reports or payments to the wrong place. Here is how Illinois divides business oversight and tax collection.

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Registering with IDOR and IDES on Form REG-1

According to the Illinois Department of Revenue, you must register your business if you conduct business in Illinois or with Illinois customers. This rule applies to corporations, partnerships, LLCs, and sole proprietors (including an individual, married couple, or civil union), as well as exempt organizations or government agencies that withhold Illinois Income Tax for Illinois employees. You must complete this registration before you make any purchases, make any sales, or hire an employee.

You register using Form REG-1 (R-07/26), the Illinois Business Registration Application. How you submit Form REG-1 determines how quickly you get your tax account:

• Online through MyTax Illinois: Submitting Form REG-1 at mytax.illinois.gov is the fastest method and lets you register simultaneously with the Illinois Department of Employment Security (IDES) inside MyTax Illinois.
• By mail or in person: Mailing a paper Form REG-1 to the Central Registration Division in Springfield takes 4 to 6 weeks to process on a first come, first served basis, and IDOR advises allowing 6 to 8 weeks when mailing Form REG-1 with attached schedules. You can also pick up a paper form and get assistance at a local IDOR office.

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• ilsos.gov: Business Services Official Website of the Illinois Secretary of State Here's how you know

Form REG-1 schedules and filing cadence

Depending on how your business is structured and what you sell, Form REG-1 requires supporting schedules. Step 2 of Form REG-1 requires the Social Security numbers and home addresses of owners, general partners, corporate officers (president, secretary, and treasurer for non-publicly traded corporations, or chief operating officer and chief financial officer for publicly traded corporations), or LLC managers and members.

If you have additional owners, multiple sites, or employees, you attach the matching schedule to your application, and then follow the required filing cadence for each account:

• Schedule REG-UI-1: Report to Determine Liability Under the UI Act, required if you answer yes to having Illinois employees.
• Schedule REG-1-L: Illinois Business Site Location Information, required if you have multiple Illinois locations, hold inventory in Illinois, collect local sales tax from Illinois sites, rent hotel rooms for less than 30 days, or rent vehicles for one year or less.
• Schedule REG-1-O and Schedule REG-1-R: Schedule REG-1-O is used when you need to identify additional owners or officers beyond the spaces on the main form. Schedule REG-1-R (Responsible Party Information) is attached if someone other than the person signing Step 4 is responsible for filing returns and paying taxes.
• Schedule REG-1-MKP and activity-specific schedules: Schedule REG-1-MKP is required for marketplace facilitators, and IDOR provides additional REG-1 schedules for regulated activities such as liquor, tobacco, electricity, gas use, medical cannabis, telecommunications, and motor or aviation fuel.
• Ongoing filing cadence and payments: Once registered, businesses file annual income tax returns (or annual information returns for partnerships), make regular estimated tax payments during the year as income is earned, file monthly or quarterly IDES unemployment wage reports (Form UI-3/40), file quarterly federal payroll returns (Form 941) and annual W-2s, and file annual entity reports with the Illinois Secretary of State.

• tax.illinois.gov: Illinois Department of Revenue
• IRS: Business taxes

How to get your Certificate of Registration

Once IDOR approves your application, you receive a taxpayer ID and, if applicable, a Certificate of Registration or License. IDOR no longer prints and mails paper certificates for most tax types. This includes the Retailers' Occupation Tax Act, Use Tax Act, Service Use Tax Act, and Service Occupation Tax Act. It also includes the Hotel Operators' Occupation Tax Act, Automobile Renting Occupation and Use Tax Act, Rental Purchase Agreement Occupation and Use Tax Act, Parking Excise Tax Act, Dry-Cleaning Solvents Tax, and cannabis taxes.

Instead, IDOR issues these certificates electronically. To download and print yours, log in to your MyTax Illinois account, select "View more account options," and click "View Account Letters" in the "Letters and Messages" panel. If you cannot print it yourself, you can contact the IDOR Central Registration Division by phone at 217-785-3707, by email at REV.CRD@Illinois.gov, or by mail to request a paper copy.

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Federal and Illinois business income taxes

Per the IRS (as of April 2026), the business structure you operate determines which returns you file. All businesses except partnerships must file an annual income tax return, while partnerships file an annual information return. On Form REG-1, Illinois recognizes proprietorships, partnerships, trusts or estates, corporations, S corporations (Subchapter S corporations), governmental units, not-for-profit organizations, and LLCs (classified as a corporation, partnership, S corporation, or single-member disregarded entity). If your business is part of a unitary group, you must also identify the federal employer identification number (FEIN) of the designated agent responsible for filing your Illinois income tax return.

Federal income tax is a pay-as-you-go system. If you work for yourself and have net earnings from self-employment of $400 or more, the IRS requires you to pay self-employment tax (Social Security and Medicare) and file Schedule SE with Form 1040 or 1040-SR. Church employees of organizations that elected an exemption from Social Security and Medicare taxes are subject to self-employment tax if they receive $108.28 or more in wages. Because self-employed owners do not have tax withheld from a paycheck, you generally make regular payments of estimated tax during the year for both income tax and self-employment tax.

In Illinois, sole proprietors and individual filers can submit Form IL-1040 (Individual Income Tax Return) and look up estimated payments (IL-1040-ES) or extension payments (IL-505-I) through MyTax Illinois. For business entities, you submit your annual Illinois Business Income Tax return using Modernized e-File (MeF), approved third-party tax-preparation software, or paper forms.

• IRS: Business taxes
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Sales, use, and occupation taxes in Illinois

Illinois taxes retail sales and the use of tangible personal property through a series of occupation and use tax acts. When you fill out Step 3 of Form REG-1, you must indicate whether you sell, lease, or rent tangible personal property at retail or wholesale, or whether you transfer tangible personal property as part of a sale of service (which falls under the Service Occupation and Use Tax).

How you report and remit these taxes to IDOR depends on your registration status and where your business is located:

• Form ST-1 and Form ST-2 (Sales and Use Taxes): Registered retailers and service businesses file Form ST-1 (and Form ST-2 for multiple locations) using MyTax Illinois, automated bulk filing, third-party software, or paper. If you are registered to file Form ST-1, you must report any use tax liability on Form ST-1.
• Form ST-44 (Use Tax): If your supplier does not collect Illinois sales tax on merchandise your business uses or consumes in Illinois, you owe self-assessed use tax. IDOR specifies that Form ST-44 should only be used by businesses that are not required to register for sales and use taxes.
• Out-of-state remote retailers and marketplace facilitators: On Form REG-1, out-of-state sellers must indicate if they have an Illinois physical presence (an office, facility, employees, representatives, or inventory in Illinois) or if they meet the annual sales threshold from their own sales to Illinois purchasers.
• Hotel operators and hotel marketplace facilitators: Under the Hotel Operators' Occupation Tax rules on Form REG-1, businesses renting hotel rooms for less than 30 days must attach Schedule REG-1-L and indicate if they are registering as a re-renter of hotel rooms or facilitating rentals through a marketplace.
• Motor vehicles and watercraft: Retailers covered by the Electronic Registration and Title Program for cars, motorcycles, ATVs, trailers, watercraft, aircraft, and manufactured homes use Forms ST-556, ST-556-LSE, RUT-25, RUT-25-LSE, and RUT-50.

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Employer payroll withholding and IDES unemployment taxes

Hiring employees in Illinois triggers tax responsibilities at both the federal and state levels. At the federal level, the IRS requires employers to manage Social Security and Medicare taxes, federal income tax withholding (reported on Form 941, Employer's Quarterly Federal Tax Return, and Form W-2), and federal unemployment (FUTA) tax.

At the state level, you report payroll to both IDOR and IDES. For Illinois Income Tax withholding, IDOR mandates the electronic filing of Forms W-2, W-2c, and W-2G (and Form 1099-K in some situations) through its Electronic W-2 and 1099 Transmittal Program or Federal/State Employment Taxes (FSET) bulk filing.

For state unemployment insurance, the Illinois Department of Employment Security (IDES) requires every business with employees in Illinois to register and file unemployment insurance contribution and wage reports (Form UI-3/40) each quarter. You can file monthly or quarterly wage reports, report zero quarterly wages, view annual rates, and pay UI taxes directly through MyTax Illinois. Under the Illinois Unemployment Insurance Act, your liability to pay UI contributions starts as soon as you meet the threshold for your organization type:

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• IRS: Business taxes

Personal liability and keeping your accounts updated

Illinois enforces strict personal liability rules for payroll and tax compliance. When you sign Step 4 of Form REG-1, you attest under penalties of perjury that you are personally responsible for filing returns and paying all taxes due unless you attach Schedule REG-1-R naming another responsible party.

Similarly, IDES warns that the Illinois Unemployment Insurance Act holds any corporate officer or employee who has control, supervision, or responsibility for filing UI reports or paying contributions personally liable if they willfully fail to file or pay. If an employer fails to file a report or pay contributions, penalties, or interest when due, IDES looks to corporate officers and responsible individuals for payment. Unpaid balances can result in liens on personal homes, autos, boats, and property, as well as levies on personal bank accounts, increased employer UI taxes, field audits, and mandatory appeal hearings.

To avoid missed notices or processing errors, IDOR requires you to update your registration electronically through MyTax Illinois, by phone at 217-785-3707, or at an IDOR office whenever your business address, ownership, locations, or tax responsibilities change.

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• tax.illinois.gov: Illinois Department of Revenue

Specialty and excise taxes

Certain industries must register for and file excise or specialty tax returns at both the state and federal levels. In Illinois, Form REG-1 and IDOR filing rules cover motor fuel and International Fuel Tax Agreement (IFTA) carriers. New IFTA carriers apply for licenses and decals using Form MFUT-12, and carriers file for single trip permits using IDR-277. Illinois specialty rules also cover retail soft drinks in Chicago, tire user fees, vending machines, liquor warehousing and retail, and cigarettes and tobacco. Finally, IDOR regulates dry-cleaning facilities and solvent suppliers, coin-operated amusement devices, medical and adult-use cannabis, and utility service providers for electricity, natural gas, telecommunications, and water or sewer services.

At the federal level, the IRS requires businesses that manufacture or sell specific goods or operate heavy equipment to file federal excise returns. These include Form 720 (for environmental, communications, air transportation, fuel, retail heavy truck or trailer, and manufacturers taxes) and Form 2290 (for highway motor vehicles with a taxable gross weight of 55,000 pounds or more).

• IRS: Business taxes
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Annual reports with the Illinois Secretary of State

Tax filings with IDOR and IDES are separate from your legal entity filings. The Illinois Secretary of State Department of Business Services (with flagship offices in Springfield and Chicago) oversees all domestic and foreign business entities formed or registered to do business in Illinois, including Corporations, Not-for-Profit Corporations (NFPs), Limited Liability Companies (LLCs), Limited Partnerships (LPs), and Limited Liability Partnerships (LLPs).

Once your entity is formed, you must use the Secretary of State's online portal to file annual reports for your Corporation, NFP, or LLC, obtain Certificates of Good Standing, or process entity reinstatements and terminations. You also need your Illinois Secretary of State identification number when completing Step 1, Line 7 of IDOR Form REG-1.

• ilsos.gov: Business Services Official Website of the Illinois Secretary of State Here's how you know
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Illinois new business tax setup checklist

Use this step-by-step plan written by our team to set up your Illinois business tax accounts in the right order without triggering processing delays.

Case study: Suppose a newly formed Illinois LLC opens a retail shop in Chicago and hires one part-time employee earning $2,000 in their first calendar quarter. Because the shop sells merchandise at retail and exceeds the $1,500 quarterly wage threshold for for-profit employers, the owner registers online via Form REG-1 on MyTax Illinois before buying inventory, making a sale, or running payroll, attaching Schedule REG-1-L for the shop site and Schedule REG-UI-1 for IDES unemployment insurance. Once approved, the owner downloads the electronic Retailers' Occupation Tax Certificate of Registration from MyTax Illinois, uses MyTax Illinois for Form ST-1 sales tax and quarterly Form UI-3/40 unemployment filings, and uses Modernized e-File (MeF) or tax software for the annual Illinois Business Income Tax return.

• Step 1: Form or register your legal entity (Corporation, LLC, LP, LLP, or NFP) with the Illinois Secretary of State Department of Business Services and save your Illinois Secretary of State identification number.
• Step 2: Apply for a Federal Employer Identification Number (FEIN) with the IRS (sole proprietors without an FEIN will use their Social Security number on Form REG-1).
• Step 3: Before making any purchases, sales, or hiring an employee, submit Form REG-1 online through MyTax Illinois.
• Step 4: If you are hiring Illinois employees, complete Schedule REG-UI-1 inside MyTax Illinois at the same time so you are registered with both IDOR for income tax withholding and IDES for quarterly UI-3/40 unemployment wage reporting.
• Step 5: Log in to MyTax Illinois after approval, open "View more account options," and download your electronic Certificate of Registration or License from "View Account Letters."
• Step 6: Set up third-party software or a tax preparer using Modernized e-File (MeF) for your annual Illinois Business Income Tax return.
• Aldro is the cheapest way to get your business taxes done: $399 flat, with bookkeeping at $20 a month. The flat price covers everything tax for the year (every federal and state or provincial business return: Schedule C, 1065, 1120-S, 1120 and state returns), multi-state returns at the same price, the owner's personal return when the business income needs it, city and local business returns and state franchise tax reports included, 1099-NEC slips included, and extensions and quarterly estimate reminders included. Bookkeeping covers unlimited bank and card accounts, monthly reconciliation and statements, but not payroll processing or sales-tax filing.

• tax.illinois.gov: Illinois Department of Revenue
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