Two men are now competing to replace him. They're Democrat Gregory Whalen and Republican James Mendrick.
WATCH: Hear from Republican candidate James Mendrick
Mendrick is a 22 year veteran of the DuPage County Sheriff's department.
He's held a variety of positions within the department and currently serves as the Patrol commander.
Mendrick says he would bring that experience to the job if elected Sheriff.
Democrat Gregory Whalen is currently a Lieutenant with the Glencoe Department of Public Safety which cross trains its staff in all three public safety professions: law enforcement, fire and emergency medical services.
Whalen says if elected, he would have the ability to bring all public safety agencies together during major incidents.