Illinois is making it harder than ever to ignore your business structure. In 2026, the state permanently extended its Pass-Through Entity Tax (PTET) — removing the scheduled sunset and locking in a planning lever that affects both LLCs and S-Corps alike. That legislative move is a good reminder: the entity you form today shapes your tax bill, your investor conversations, and your compliance obligations for years to come. If you are still asking S-Corp or LLC? you are asking the right question — and the answer genuinely depends on where your business is headed.

This is one of the most common questions Illinois founders bring to Fitter Law. So let’s work through it plainly, without the jargon.

The Basics: What Each Structure Actually Is

An LLC (Limited Liability Company) is a flexible legal entity that separates your personal assets from your business debts and obligations. By default, a single-member LLC is taxed like a sole proprietorship and a multi-member LLC is taxed like a partnership — both are pass-through structures. The LLC itself pays no federal income tax; profit flows to the owner(s) and gets reported on their personal returns.

An S-Corporation is not a separate type of legal entity under state law — it is a federal tax election. You form an LLC or a corporation first, then file IRS Form 2553 to be taxed as an S-Corp. Once that election is in place, the entity is still a pass-through for income tax purposes, but the mechanics of how owners pay self-employment tax change significantly.

In Illinois, both structures are recognized and widely used by startups and small businesses. The right choice depends on three things: your current revenue, your growth plans, and whether you intend to raise outside investment.

The Real Difference: Self-Employment Tax

For most founders, the S-Corp conversation starts and ends with self-employment tax — and for good reason.

When you operate as an LLC taxed as a sole proprietorship or partnership, all of your net business profit is subject to self-employment (SE) tax, which runs 15.3% on the first $168,600 of income (2024 rate) and 2.9% above that. On $150,000 of net profit, that is a meaningful line item.

An S-Corp election changes that equation. As an S-Corp owner-employee, you split your income into two buckets:

• Reasonable salary — subject to payroll taxes (both the employee and employer share of FICA)
• Distributions — passed through to you as profit, not subject to self-employment tax

The savings can be real. The key variable is what the IRS considers a “reasonable salary” for your role. You cannot pay yourself $1 in salary and take $500,000 in distributions — the IRS will recharacterize that. But if your business generates, say, $200,000 in profit and a reasonable salary for your position is $90,000, the remaining $110,000 in distributions escapes self-employment tax. At 15.3%, that is real money.

The catch: S-Corp status comes with payroll compliance obligations. You must run an actual payroll, file quarterly payroll tax returns, and maintain documentation of your reasonable compensation decision. That adds cost and complexity — typically a few hundred to a few thousand dollars per year in accounting and payroll service fees. The S-Corp election makes sense when the SE tax savings exceed those added costs, which generally starts happening in the $50,000–$80,000+ net profit range. Below that threshold, the overhead often outweighs the benefit.

What Illinois Adds to the Equation

Federal tax treatment is only part of the story. Illinois has its own layer that founders often miss.

Personal Property Replacement Tax (PPRT)

Illinois imposes a 1.5% Personal Property Replacement Tax on S-corporation net income at the entity level — before income flows through to shareholders. This is separate from the 7% Illinois corporate income tax, which S-Corps are not subject to. By contrast, C-Corps in Illinois face a combined 9.5% entity-level rate (7% income tax + 2.5% PPRT). LLCs taxed as partnerships also pay the PPRT, but at a different rate structure.

The practical upshot: S-Corps still enjoy a significant Illinois tax advantage over C-Corps, but they are not entirely free of entity-level state tax. Budget for the 1.5% PPRT when you are modeling your Illinois tax picture.

The Illinois Franchise Tax

Illinois corporations — including entities taxed as S-Corps that are organized as corporations — are subject to the Illinois franchise tax. The planned full repeal of this tax was reversed by the legislature, and it remains in effect indefinitely. As of 2025, the first $10,000 in annual franchise tax liability is exempt, which shields most early-stage startups from a meaningful hit. But it is a real compliance obligation that LLCs organized as LLCs (rather than as corporations) do not face in the same way.

The Pass-Through Entity Tax Election

Illinois permanently extended its PTET in late 2025. This is an optional entity-level tax of 4.95% on net income for S-Corps, partnerships, and LLCs taxed as partnerships. The corresponding credit flows through to owners and can help high-income founders work around the $10,000 federal SALT deduction cap. It is not the right move for everyone, but it is worth a conversation with your attorney and accountant at formation — especially if your Illinois income is significant.

The Investor Problem with S-Corps

Here is where the S-Corp election can quietly create a major problem for founders with growth ambitions: S-Corps are structurally incompatible with most venture capital investment.

Under IRS rules, S-Corps can only have:

• Up to 100 shareholders
• One class of stock (no preferred equity)
• Only U.S. citizen or permanent resident individual shareholders — no corporations, LLCs, or most trusts as owners

That last point is the deal-breaker. VC funds and institutional investors are almost always organized as LLCs or limited partnerships — entities that cannot hold S-Corp stock without terminating the S election. The moment you bring in outside investment from an entity investor, or issue preferred stock to a VC, your S-Corp election is blown. You become a C-Corp for tax purposes from that date forward, with no transition period.

Even for founders who are not yet thinking about institutional venture capital, the S-Corp structure limits your flexibility. Convertible notes and SAFEs — the most common seed-stage financing instruments — typically convert into preferred equity at a later round. Preferred equity = multiple classes of stock = end of S-Corp status.

If you have any real intention of raising outside investment, the better path is usually to form a Delaware C-Corp from the start, not to form an S-Corp and convert later. The conversion can be done, but it creates unnecessary complexity and potential tax exposure.

LLC vs. S-Corp: A Quick Decision Framework

Here is how to think about it at a high level — though the right answer for your specific situation requires a real conversation with counsel:

• Form an LLC (taxed as a disregarded entity or partnership) if you are early-stage, pre-revenue or low-revenue, not yet generating meaningful profit, and want maximum simplicity and flexibility. An LLC operating agreement gives you enormous flexibility in how you structure ownership, profit-sharing, and management. You can always make an S-Corp election later once the tax savings justify the overhead.
• Consider an S-Corp election for your LLC if you are generating consistent net profit in the $80,000–$100,000+ range, you are paying too much in self-employment tax, and you have no near-term plans to raise institutional equity. The election can be made on an existing LLC — you do not need to start over.
• Form a Delaware C-Corp if you are building a venture-backed startup, expect to raise a seed round or Series A, or need the clean cap table and governance structure investors expect. Skip the S-Corp entirely.

Common Mistakes Illinois Founders Make

• Making the S-Corp election too early. Below roughly $50,000–$80,000 in net profit, the payroll compliance costs often eat the tax savings.
• Forming as an S-Corp and then raising money. This terminates the election and creates a tax headache at the worst possible time — during a financing round.
• Ignoring the Illinois-specific tax layer. The PPRT and franchise tax are real obligations that generic online formation services do not walk you through.
• Using a one-size-fits-all template. Illinois has specific requirements for LLC operating agreements and corporate governance documents. Generic documents from national platforms often miss Illinois-specific provisions.

Get This Decision Right From the Start

Entity formation is one of the few decisions in your startup’s life that is genuinely hard to undo cleanly. The wrong structure costs you in taxes, compliance overhead, or — worst case — in a failed fundraising round when investors discover a structural problem.

At Fitter Law, we work with Illinois founders on business entity formation, operating agreements, and the strategic questions that come before you file anything with the Secretary of State’s office. If you are weighing S-Corp vs. LLC — or wondering whether a Delaware C-Corp makes more sense for where you are headed — view our flat-fee business law packages.

This article is for informational purposes only and does not constitute legal advice. No attorney-client relationship is created by reading this post. Tax rules change frequently — consult a licensed Illinois attorney and a qualified CPA before making entity formation decisions.