EIN Guide for an Illinois Limited Partnership

An Employer Identification Number, issued by the IRS, is a nine-digit federal tax identifier for a business. Think of it as a Social Security number for your business: it identifies the partnership to the IRS on tax filings, to banks when you open accounts, and to any agency or counterparty that needs a tax ID for the entity.

It identifies the LP, not you

The EIN belongs to the partnership as a distinct entity. That separation is exactly what you want — your LP is a legal entity apart from its partners, and giving it its own tax ID reinforces that it is not simply an extension of any individual. For a limited partnership with multiple partners and a partnership tax return, the EIN is not optional in any practical sense; it is how the entity is identified on its filings.

The EIN is always free

The IRS issues EINs at no cost. This is worth stating plainly because plenty of services charge a fee to "get your EIN," which can give the impression there is a government charge behind it. There is not. The IRS charge is zero; any fee is purely for the convenience of someone completing the short application on your behalf.

Unlike a single-member LLC, which can sometimes get by on the owner's Social Security number, a limited partnership realistically needs its own EIN from the start. A few reasons make it effectively mandatory.

The partnership files its own return

A limited partnership is a pass-through entity that files an informational federal return, Form 1065, and issues a Schedule K-1 to each partner reporting their share of income. That return is filed under the partnership's EIN — the entity has to have one to file at all. This alone settles the question for nearly every LP.

Banks require it

No bank will open an account in the partnership's name without an EIN. Since keeping partnership money separate from the partners' personal money is essential — both for clean books and for preserving the LP's structure — the business bank account is a must, and the EIN is the prerequisite for it.

Employees and payroll

If the LP hires employees, the EIN is what you use for federal payroll tax deposits and employment tax filings. Even LPs that start with no employees often plan to add them, and the EIN is in place from the beginning.

Vendors and contracts

Counterparties frequently ask for the LP's tax ID on contracts, W-9s, and payment setups. Handing over the partnership's EIN — rather than an individual partner's Social Security number — keeps personal identifiers out of business paperwork.

Getting an EIN is quick and free, and for most partnerships it takes about ten minutes online.

Apply online at IRS.gov

The fastest route is the IRS EIN Assistant on IRS.gov. You complete a short application about the partnership, and the EIN is issued immediately at the end — you can download the confirmation and use the number the same day. The online tool is available during the IRS's posted hours.

What you will need

• The legal name of the limited partnership as filed
• The partnership's principal business address
• The name and taxpayer identification number of the responsible party (generally a general partner, or a person who controls the entity)
• Basic information about the LP's activity and structure

The responsible party requirement

The IRS requires a "responsible party" — a real person with a U.S. Social Security number or ITIN — to complete the online application. For an LP, this is typically a general partner. Where the general partner is itself an entity, the responsible party is generally an individual who ultimately controls it.

No SSN or ITIN? Apply on paper

Applicants without a U.S. SSN or ITIN cannot use the online tool and instead file Form SS-4 by fax or mail. This route takes longer than the instant online issuance, so plan ahead if it applies to your situation.

Timing the EIN correctly saves rework, and there is a natural point for it in the formation sequence.

Form the LP first

The cleanest order is to file your Certificate of Limited Partnership and have the LP legally exist before applying for the EIN. The application asks for the partnership's legal name and details, and getting the entity on record first means the EIN attaches to a partnership that actually exists under that exact name. Applying before the entity is formed can create mismatches you then have to untangle.

Then EIN, then bank account

Once the LP is formed and the EIN is issued, you have what the bank needs to open the partnership's account. The common sequence — form the LP, get the EIN, open the bank account, then handle the partnership agreement and any state tax registrations — keeps each step supplied with what the previous one produced.

Keep the confirmation

When the IRS issues the EIN, save the confirmation letter (the CP 575, or the online download). Banks and counterparties sometimes ask to see it, and if you ever misplace the number, having the original confirmation avoids a call to the IRS to recover it.

Mainstay Filing's core job is the state formation — preparing and submitting your Certificate of Limited Partnership and providing registered agent service. The EIN is a federal item that sits alongside that, and it is genuinely simple to obtain yourself, free, in about ten minutes at IRS.gov.

Because the EIN is free and fast, we are candid that this is one task many partnerships handle on their own without any downside. If you would rather not deal with the IRS application at all, some formation packages can include obtaining the EIN as a convenience — but the value there is purely the time saved, since the government charge is always zero. We will never present the EIN as a state fee or mark up a free government service.

What matters most is sequence and accuracy: form the LP under the correct legal name, then obtain the EIN so it attaches to the entity exactly as filed. We make sure the formation half is done right, which is what lets your EIN application go through cleanly on the first try.