WATCH: Chopper 7HD over Dixon High School
Dixon Police Chief Steven Howell Jr. said the officer called emergency responders, around 8 a.m. He said shots had been fired near the high school gymnasium.
Howell said the officer ran toward the shots, coming face-to-face with a 19-year-old former student holding a gun.
The former student ran away and out of the school. Police said the man turned and fired at the officer when he tried to chase him down. That's when the officer fired back, hitting and injuring the gunman.
The suspect was the only person hurt in the incident, police said. He was taken into custody and treated for his wound, which city officials said was not life-threatening. He is expected to recover.
Students and staff were quickly evacuated from the campus. Chopper 7 HD was over the scene around 9:30 a.m. and captured video of students boarding buses to be reunited with family members, who were waiting for them at a local park.
While police were quick to say there was no further threat to people in the area after the shooting, Dixon Public Schools remained on lockdown for some time.
Detectives are now trying to learn more about the man who opened fire and why he brought a gun to the school.
When officers went inside the high school, they said they saw students and teachers barricaded in their classrooms as they should have been. They have been going through training on what to do during an active-shooter situation. Authorities said they did everything right.
"A lot of things went right today, when a great many of them could have gone wrong," Dixon Mayor Liandro Arellano Jr. said at a press conference Wednesday.
Rep Adam Kinzinger was briefed on the situation by Lee County Sheriff John Simonton. Kinzinger thanked the school resource officer in a statement released Wednesday:
"As we continue to gather more information about the shooting incident at Dixon High School this morning, I extend my deepest gratitude to the Dixon Police Department, and especially the School Resource Officer (SRO) on-site, for their swift action today and for keeping our students, teachers, and our community safe."
The school resource officer is a member of the Dixon Police Department. He was placed on administrative leave, since he was involved in the shooting.
The investigation is ongoing.