Illinois Service of Process Rules: Methods, Deadlines, and Defects

The Illinois service of process rules require a plaintiff to deliver the summons and complaint to each defendant through an authorized person, using a method the statute recognizes, before an Illinois court can enter any binding order against that defendant. Service is usually made by a sheriff, a licensed private detective, or an adult specially appointed by the court, and it can be accomplished in person, through a qualifying household member, by publication, or, with a court order, electronically. Skipping steps or improvising is what turns winning cases into void judgments.

Who Is Allowed to Serve Papers

Process in Illinois is typically served by a sheriff or coroner. In counties with fewer than 2,000,000 residents, the sheriff may also use civilian employees to make service. Licensed private detectives and registered employees of licensed detective agencies can serve process statewide without a special court appointment, though they must provide a copy of their license or certificate to the sheriff of any county where they serve papers.¹

If you want anyone else to serve your papers, the court can appoint any person over 18 who is not a party to the lawsuit. That appointment, sometimes called a special process server order, requires a motion.¹

Cook County used to force plaintiffs to attempt service through the sheriff first. Public Act 103-0671, effective January 1, 2025, ended that restriction. Plaintiffs in Cook County can now hire a licensed private detective or detective agency from the outset, though the server must remit a $5 fee per service to the Cook County Sheriff through the clerk of the court.¹

How Papers Can Be Delivered

Illinois recognizes several methods. Which one you use depends on whether the defendant can be located and what kind of case you have.

Personal Service

Personal service means handing the summons and complaint directly to the defendant. It is the most reliable method because it eliminates arguments about whether the defendant actually received notice. A sheriff endorses the return on the summons itself. A private server files an affidavit stating when, where, and how the documents were delivered, and that affidavit goes into the court file.¹

Substitute Service at the Home

When the defendant cannot be reached in person, Illinois allows substitute service at the defendant’s home. The server leaves a copy of the summons with a household member who is at least 13 years old and informs that person of its contents. The server must also mail a separate copy of the summons in a sealed, postage-paid envelope to the defendant at the same address.²

Both steps are required. Leaving documents at the door without giving them to a qualifying household member does not count. Mailing alone without the in-person delivery does not count either. Defendants frequently challenge substitute service when the server cannot identify the household member by name or confirm their age, so a careful proof of service records both.

Service by Publication

When a defendant has left the state, cannot be found after a genuine search, or is hiding to avoid being served, a court may authorize service by publication. The plaintiff first files an affidavit with the clerk stating that the defendant lives outside Illinois, cannot be located after a diligent inquiry, or is concealed within the state. The affidavit must include the defendant’s last known address if available, or state that a diligent search failed to determine it.³

Once the affidavit is filed, the clerk arranges publication in a newspaper in the county where the case is pending. The notice runs once a week for three consecutive weeks and must include the case title, the case number, the names of the parties being served by publication, and the date on or after which a default may be entered. Within 10 days of the first publication, the clerk also mails a copy of the notice to the defendant at any address listed in the affidavit.³ No default or other proceeding may occur against the defendant unless the first publication ran at least 30 days before the default is sought.⁴

Courts take the diligence requirement seriously. A boilerplate affidavit stating you “couldn’t find” someone without detailing your specific steps will get rejected. Be ready to describe searches of public records, contacts with known associates, and in-person checks of the last known address.

Electronic Service by Court Order

The Illinois Supreme Court amended Rule 102 to permit service of summons by email, text message, or social media direct message when a court issues a special order finding that traditional methods are impractical. The person requesting electronic service files a motion with an affidavit explaining why they believe the defendant actively uses the specific email address, phone number, or account being targeted. A copy of the summons must also be mailed to the defendant’s last known address, and a proof of service must be filed afterward.⁵

This is not a first-resort option. Personal and substitute service generally have to be tried or shown impractical before a judge signs off. For defendants who are genuinely hard to locate physically but plainly active online, it can shortcut a case that would otherwise slide into the publication process.

Serving Corporations and LLCs

Serving a business is not the same as serving a person, and corporations and LLCs are handled slightly differently.

Private Corporations

A private corporation is served by leaving a copy of the process with its registered agent or with any officer or agent of the corporation found anywhere in the state. Corporations can also be served by publication and mailing in the same manner as individuals.⁶

Before attempting service, check the Illinois Secretary of State’s records to identify the corporation’s registered agent and registered office. If the registered agent listing is missing or outdated, you can serve any officer of the company you can locate within Illinois.

Limited Liability Companies

Service on an LLC follows a similar framework with a backstop. You serve the LLC’s registered agent. If the LLC has failed to maintain a registered agent, or its agent cannot be found at the registered office or principal place of business, you can serve the Illinois Secretary of State instead. That requires delivering a copy of the process along with the required fee, then mailing notice of the service to the LLC by certified or registered mail at both its last registered office and any other address you reasonably believe will reach the company.⁷

The Secretary of State also becomes the default agent for dissolved LLCs when a civil action is filed within five years of the dissolution certificate, and for foreign LLCs whose authorization to do business in Illinois has been revoked.⁷

Defendants Located Outside Illinois

Illinois has a broad long-arm statute. Non-residents who transacted business in Illinois, committed a harmful act here, owned property in the state, or engaged in several other enumerated activities can be sued in an Illinois court for claims arising from those activities.⁸

Once that jurisdictional link is established, the summons can be personally served on the defendant wherever they are located, with the same legal effect as service made within Illinois. For defendants outside the United States in product liability cases, service can be made through the Secretary of State with a $5 fee, followed by mailing a copy to the defendant’s last known address.⁸

Small Claims and Eviction Cases Have Their Own Rules

Some case types depart from the standard procedure. In small claims cases, the circuit clerk can serve the defendant by certified mail. It is cheaper than sheriff service and avoids hiring a private server. Sheriff service and special process servers remain available, but certified mail through the clerk is what most small claims plaintiffs choose.⁹

Eviction cases, formally called forcible entry and detainer actions, require a written demand before suit can be filed. If no one is physically present at the property, the demand can be posted on the premises. For unknown occupants without a written lease, the demand can be addressed to “unknown occupants” and posted. When serving a contract purchaser or condominium owner, the demand can be sent by certified or registered mail to the last known address, and service is effective the moment the envelope is deposited in the mail with proper postage, even if the recipient never picks it up.¹⁰

What the Defendant Has to Do After Service

Once served, a defendant has 30 days to file an appearance or answer the complaint. The day of service does not count toward the 30-day window.¹¹

Waiving Service

A plaintiff can skip formal service by sending the defendant a written request to waive it. The request must include a copy of the complaint, identify the court where it was filed, explain the consequences of agreeing or refusing, give at least 30 days to respond (60 days if the defendant is outside the country), and include a prepaid return envelope or equivalent means to send the signed waiver back.¹²

Waiving service does not waive any objection to the court’s jurisdiction or venue. A defendant who returns a timely waiver gets extra time to respond: 60 days from when the request was sent, or 90 days if it was addressed outside the United States. Defendants can refuse a waiver request, but doing so exposes them to the additional costs of formal service.¹²

Motion to Quash Bad Service

A defendant who believes service was defective can file a motion to quash service of process or to dismiss for insufficient service. The critical rule is timing: the motion has to be filed before any other pleading or motion, or the objection is waived. Filing an answer, a counterclaim, or almost any other motion first tells the court you accept its jurisdiction over you. The only exception is that you can seek an extension of time before raising your service objection without waiving it.¹³

If the facts supporting the objection are not already apparent from the court file, the motion must be backed by an affidavit laying them out. A successful motion to quash does not end the case. It just requires the plaintiff to serve again, correctly.¹³

Diligence and the Alias Summons

A plaintiff cannot file a lawsuit and then let the summons sit unserved. Illinois Supreme Court Rule 103(b) permits a court to dismiss an action when the plaintiff has failed to use reasonable diligence in getting the defendant served. This is where more claims fall apart than plaintiffs expect.

If the first summons comes back unserved, the plaintiff can request an alias summons by filing an affidavit stating that the original went unserved and that diligent attempts to accomplish service have continued. The alias summons must then be served within 30 days, or another affidavit is required to obtain a second alias.

Courts evaluate diligence using an objective, totality-of-the-circumstances test. Relevant factors include how much time has passed since filing, the specific steps the plaintiff took to locate and serve the defendant, whether the plaintiff knew the defendant’s whereabouts, how easily the defendant could have been found, whether the defendant had actual knowledge of the lawsuit despite flawed service, and any special circumstances affecting the plaintiff’s efforts.

The stakes depend on timing. A lack of diligence found before the statute of limitations runs typically results in dismissal without prejudice, so the plaintiff can refile. Once the statute of limitations has expired, dismissal is with prejudice and the claim is gone.

What Happens When Service Is Defective

Without proper service, the court never acquires personal jurisdiction over the defendant. Any judgment entered against an unserved or improperly served defendant is void, not merely voidable. A void judgment can be attacked at any time, and defendants regularly use this to unwind default judgments entered months or years earlier.

A defendant who discovers that a default judgment was entered after defective service can file a petition under Section 2-1401 of the Code of Civil Procedure to vacate the judgment. The petition is filed in the same proceeding where the judgment was entered and is supported by an affidavit covering facts not already in the court record. Section 2-1401 petitions for non-void judgments generally have to be filed within two years, but the statute specifically preserves the right to challenge a void judgment without that time restriction.¹⁴

For the plaintiff, defective service means starting over, which costs time and money. If the statute of limitations is closing in and diligence cannot be shown, the case may be dismissed with prejudice. Getting service right the first time is the cheapest part of the case.

1
Illinois General Assembly. Illinois Code 735 ILCS 5/2-202 – Persons Authorized to Serve Process
2
Illinois General Assembly. Illinois Code 735 ILCS 5/2-203 – Service on Individuals
3
Illinois General Assembly. Illinois Code 735 ILCS 5/2-206 – Service by Publication, Affidavit, Mailing, Certificate
4
FindLaw. Illinois Code 735 ILCS 5/2-207 – Period of Publication, Default
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Illinois Courts. Illinois Supreme Court Reinforces Service of Summons Allowable via Social Media, Text, and Email
6
Illinois General Assembly. Illinois Code 735 ILCS 5/2-204 – Service on Private Corporations
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FindLaw. Illinois Code 805 ILCS 180/1-50 – Service of Process on Limited Liability Company
8
Illinois General Assembly. Illinois Code 735 ILCS 5/2-209 – Act Submitting to Jurisdiction, Process
9
Illinois Courts. How to File and Serve a Small Claims Complaint and Small Claims Summons
10
Justia. Illinois Code 735 ILCS 5 Article IX – Forcible Entry and Detainer
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Illinois Supreme Court. Supreme Court Rule 101 – Summons and Original Process, Form and Issuance
12
Illinois General Assembly. Illinois Code 735 ILCS 5/2-213 – Waiver of Service
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Illinois General Assembly. Illinois Code 735 ILCS 5/2-301 – Objections to Jurisdiction Over the Person
14
Illinois General Assembly. Illinois Code 735 ILCS 5/2-1401 – Relief From Judgments