More than 60,000 students, faculty, and staff have been evacuated from the campus at Illinois State University, or Illini.
The campus in the Illinois city of Winthrop is about a half hour east of Chicago.
Illini officials say that the evacuation is due to the threat of a terrorist attack and that it is not possible to resume operations until further notice.
Illinois State University spokesperson John Pecora confirmed the lockdown to CBS News, saying that the campus was in a lockdown due to a potential threat to the university community.
Pecoras said the campus is currently undergoing an ongoing investigation into the potential threat.
Pecoras also confirmed that campus is now closed to the public.
He said the lockdown began when the school received a call from a local police department asking if they had any information on possible active shooters at the campus.
“They were concerned that there were active shooters and they had to respond immediately,” Pecoria said.
According to Pecoresos website, Illinois State is the second-largest college in the country.
The university is located about 40 miles (64 kilometers) northeast of Chicago, which is home to about 25,000 undergraduates and about 25 million graduate students.
While the lockdown was not the first time Illini has faced a potential terrorist threat, it is the largest to date, according to the University of Illinois System.
In March, a student who had attended Illini for four years died after he was shot at a campus event, and in July, a gunman opened fire at the school, killing four people and injuring 11 others.
University of Illinois officials have said that the shooter was a graduate student, and a source told ABC News that the gunman, identified as Jeremy Christian, had been suspended from the university for four months for domestic violence and alcohol-related offenses.
Officials say that Christian’s arrest is the first in the shooting spree at Illinois state, but the investigation is ongoing.
At the time of the shooting, Illini’s campus was filled with students and staff, who were gathered in the courtyard of the student union for a candlelight vigil.
Earlier this month, a man in a ski mask opened fire on a campus parade, killing a security guard.
Police said that one of the men in the mask was the same person who was involved in the attack on Illini, who is also a graduate of the university.