The Normal Community High School says on its website that nobody was hurt in the Friday morning incident.
Police say one of the two students in custody is a 14-year-old boy. Police are treating the school campus as a crime scene.
Classes have been dismissed and students have been taken to a church to be collected by their parents. Other schools in Normal, just north of Bloomington, remain open.
Police aren't allowing students to drive their vehicles away.
Bloomington is 135 miles southwest of Chicago.
