It happened last Friday in west suburban Addison.
Authorities say it was all just a big lie, that reports by a student that there was an intruder inside Indian Trail Junior High School were never true.
"During the course of the investigation, the student admitted fabricating the story," said Addison Police Department Director Bill Hayden.
Monday afternoon, Addison police and school officials confirmed that the lockdown of Indian Trail Junior High School was the result of a hoax.
"We have learned from this incident of the importance of making sure that students and anybody involved in an incident tell the truth and do reach out for help," said Addison School District 124 Superintendent John Langton.
It was Friday morning when authorities got a 911 call from the middle school about a female student found restrained in a bathroom.
Eighth grader Sydney Ludwig was in class when police descended on the building and a nearby elementary school looking for an intruder the student claimed had tied her up:
"I guess she was in there and then the girl that found her got help for her and then she came to class a couple minutes late and then we were all wondering what happened and then like five minutes later we went on a soft lockdown and then like three minutes after that we were in hard lockdown."
Students were eventually released in the afternoon.
Monday, authorities say their investigation shows there was never any danger.
"The guardians were extremely cooperative," said Hayden, "and they were a big part of this situation, helping resolve it and get to the truth."
Police officials refused to offer details about the incident or the student who could face disciplinary action ranging from a reprimand to expulsion.
Still, some parents expressed concern about the incident.
"I'm relieved, a little angry that this happened to all of them, because it's traumatic," said Valerie Ludwig, "but I'm glad it was not real."
Police and school officials are trying to a positive spin on the situation, saying it proves their emergency response procedures work well. They'll still look at what happened Friday to see where they can improve.
Officials also add that they would make counselors available to students and staff when they return to class Tuesday.