Illinois DOR Income Tax Audit Protest

The situation

David, 48, is a Chicago-based CPA who also owns a 40% interest in a medical staffing partnership (Midwest HealthStaff Partners LP). The partnership operates in Illinois, Wisconsin, and Minnesota. In 2023, the partnership earned $2.8M in income; David's allocable share: $1.12M.

IDOR issued a Notice of Proposed Deficiency for David's 2023 personal income return: "Additional Illinois Income Tax Due: $31,440, for failure to properly source Illinois-source income from Midwest HealthStaff Partners LP."

IDOR's position: Midwest HealthStaff Partners allocates income based on physical locations of staffing contracts (roughly 55% in Illinois). IDOR agrees with the allocation methodology but disagrees with the specific contracts David categorized as non-Illinois, IDOR reclassified 8 client contracts from "Minnesota" to "Illinois" based on the contracts' billing addresses (even though services were physically performed in Minnesota).

David has 60 days to protest. Since $31,440 exceeds the $15,000 threshold, David can file a petition with the Illinois Independent Tax Tribunal.

What David needs to understand: (a) The Illinois income allocation dispute is about where services were PERFORMED, not where clients are billed. Illinois-source income for service-based partnerships is sourced to where the services are performed (35 ILCS 5/304(a)(3)(C-5) for apportionment). If Midwest HealthStaff's Minnesota contracts involved healthcare workers physically stationed in Minnesota facilities, the income is Minnesota-source regardless of billing addresses. (b) The ICB informal conference may resolve this quickly. Before petitioning ITT, David should try the Informal Conference Board, it's free and informal. If ICB can review the specific contracts and confirm the physical service location evidence, it may withdraw the proposed reclassification. (c) The Illinois Independent Tax Tribunal provides genuine independent review if ICB fails. (d) Horwood Marcus & Berk quoted David $9,500 for IDOR protest and ITT representation. The partnership income allocation analysis and ICB/ITT protest letter are structured legal tasks David can substantially build himself.

Second portrait: Sarah, 32, is a marketing consultant (sole proprietor, $148,000 2023 revenue) who moved from Chicago to Nashville, TN in April 2023. She continued working remotely for Chicago clients through December 2023. IDOR issued a Notice of Proposed Deficiency for $17,640, IDOR's position: Sarah was an Illinois resident for the first 4 months of 2023 (January-April) and should have reported her full-year self-employment income as Illinois-source during the residency period, plus she continued performing services for Illinois clients post-departure.

Sarah's defense: Illinois income tax for a part-year resident applies only to income earned during the Illinois residency period PLUS Illinois-source income earned as a nonresident. Sarah's remote work for Illinois clients while living in Tennessee is NOT Illinois-source income, Illinois sources service income to where the services are PERFORMED, and Sarah performed post-April work in Tennessee.

Who receives this

Illinois taxpayers receiving IDOR audit notices with proposed income tax adjustments. Primary segments: (1) Illinois partnership and S-corp partners/shareholders with complex PTE income allocation; (2) Part-year residents who left Illinois and continue serving Illinois clients remotely; (3) Illinois employers and employees with remote work withholding disputes; (4) Self-employed individuals disputing deduction disallowances. Scale: Illinois is the 6th largest US state economy; IDOR conducts tens of thousands of income tax audits annually.

Why the agency will not advise you

IDOR cannot advise taxpayers how to contest its own audit notices. ITT is genuinely independent (35 ILCS 1010/1-1). 60-day deadline. Professional market: $3,000-$20,000. Illinois PTE elections (Act 395, 2021) created new compliance complexity that generates audit disputes well-suited to structured self-serve analysis.

Key facts, with sources

• The Illinois Department of Revenue conducts income tax audits of individuals, corporations, and pass-through entities. When IDOR issues a notice with protest rights following an audit, the taxpayer has 60 days to choose from several protest paths. For disputes where the tax liability (excluding penalties and interest) exceeds $15,000 OR where total penalties and interest exceed $15,000, the taxpayer may file a petition with the Illinois Independent Tax Tribunal (ITT), a genuinely independent state agency created by the Tax Tribunal Act (35 ILCS 1010/1-1 et seq.), NOT part of IDOR. ITT Administrative Law Judges are not IDOR employees; ITT decisions are appealable to the Illinois Appellate Court. For disputes under the $15,000 threshold, the taxpayer requests an administrative hearing within IDOR (administrative law judge employed by IDOR, less independent). IDOR also offers two pre-notice informal options: the Informal Conference Board (ICB), which reviews unagreed audit adjustments before a statutory notice is issued, and the Fast Track Resolution (FTR) program, a one-day mediated conference held while the case is still with the Audit Bureau. Key Illinois income tax audit types: (1) Pass-through entity (PTE) income allocation disputes, the 2021 Illinois PTE election (Act 395, 35 ILCS 5/502.1) created new compliance complexity for partnership and S-corp income; (2) Remote worker withholding, Illinois requires withholding for employees working remotely from Illinois, with nexus disputes for short-term remote work periods; (3) Nonresident income allocation, Illinois-source income for nonresidents performing services in Illinois. Source: Your Options to Dispute IDOR Deficiencies — Illinois DOR · Illinois Independent Tax Tribunal · Illinois Notice of Tax Liability 60-Day Guide — Sales Tax Helper

When to bring in a professional

Self-serve responses fit routine cases: clear facts, amounts a business can absorb, and a deadline still ahead of you. Bring in a licensed professional when the amount at stake is large relative to their fee, the facts are genuinely disputed, criminal exposure is possible, or the deadline has already passed. A short paid consultation to sanity-check your plan is often worth it even when you handle the filing yourself.

All sources for this guide

1. Your Options to Dispute IDOR Deficiencies — Illinois DOR
2. Illinois Independent Tax Tribunal
3. Illinois Notice of Tax Liability 60-Day Guide — Sales Tax Helper