The short answer
Service of process is the formal delivery of the summons and complaint to the defendant. The summons says when the defendant must respond. Until a defendant is properly served, the court generally cannot enter a judgment against it.
Where it fits in your case
It happens right after filing. In Illinois state court, a defendant usually must appear within 30 days of service. In federal court, an answer or motion is generally due 21 days after service.
What to expect
Individuals are served in person or by leaving the papers with a household member 13 or older, followed by mailing.
Companies are served through their registered agent or an officer or agent.
Diligence matters. Under Supreme Court Rule 103(b), a plaintiff who does not diligently serve can have the case dismissed, sometimes with prejudice.
What we need from you
If you were served: the papers, who received them, and when. If you are suing: the defendant’s exact legal name and registered agent.
Common misconceptions
“I heard about the case, so I was served.” Actual knowledge does not replace proper service.
“Ignoring it buys time.” It usually leads to a default judgment.