The search of the high school found no weapon or bomb. No students were taken into custody, but some were questioned at the school.
Students were released from the football field to parents or buses. Police and school officials escorted some students back into the building, like those who were in gym class at the time of the incident and needed to get purses or bookbags.
Parent/teacher conferences will continue as scheduled on Wednesday. No students will be in class across the district.
Police planned to do a final sweep of the school, Det. Sgt. Todd Wilson said.
1:45 p.m. Update:
School is slated to be dismissed at 2:20 p.m., per the district's Facebook page. All evening activities are canceled, including sporting practices and parent/teacher conferences.
Students are still on the football field. Mother Amy Young told Patch she's glad the district kept parents informed through various means, including robo calls and updates on Facebook.
"I'd rather they overreact than under react," she said.
Jason Lively, a parent, came to school to wait for his daughter. She has a cellphone, but her father believes she doesn't currently have access to it.
Lively said he's pleased with the response of the school district so far.
"It's likely just a hoax but you never know," he said. "You can't be too cautious."
The St. Charles School District will send out an AlertNow message to parents when students are dismissed, according to a Facebook message from the district. Parents at the scene will be able to pick up their children. All other students will be allowed to leave the way they came to school.
Det. Sgt. Todd Wilson, of the , told Patch that the threatening note was found today in a locker.
"It was given to the SRO (school resource officer), and the decision was made to put the school on lockdown," Wilson said.
According to Wilson, the note made threats against the building, some students and teachers.
The school was searched for anything out of the ordinary, and students were evacuated to the football field after going through a metal detector.
Wilson said another thorough sweep will be made once all the students have exited the building.
According to 's Facebook page, students will be dismissed to leave however they came to school—car, walking or bus.
Many students exited the building without backpacks and purses. It is not yet known when they will be allowed in to get their belongings.
12:30 p.m. Update:
Maria Gonzalez, who was outside the school, heard from her daughter and grandson who are inside.
Gonzalez's daughter said the students had to go through a metal detector before exiting the school onto the football field.
For parents waiting outside, cellphones are a key link to their children.
Many parents heard the news first from their children before the district sent out a robo call.
remains on lockdown at noon, after a threat was reported around 9:15 a.m. today.
Students were beginning to move to the football field, but the building remained secure while officials investigated the threat.
According to the St. Louis Post-Dispatch, a student found a threatening letter and reported it to school officials.
Students have been able to contact parents, according to various reports.
Patch will have updates as the become available.