The sheriff's department says Daniel McDade of Lombard was on bail for DUI and was ordered to go to the courthouse for a drug test.
Police say McDade became upset and started posting threatening messages on Facebook, stating he was going to shoot up the courthouse in a "Columbine-type" style.
Detectives found the 31-year-old in Denver, Colorado, where he was taken into custody.
McDade is now awaiting extradition back to Illinois.
