I recently retired in Central Illinois after over 30 years in as a Deputy Sheriff. Our own Department did not maintain the type of records that you are asking about. Some Departments have Public Relations Officers who might be able to help, but that woudl require knowing where your relatives were employed and contacting each one directly. Illinois started an organized training program in the late 1960, called Police Training Institue, at the University of Illinois in Urbana-Champaign. Illinois State Police have their own Training Academy in Springfield and the Chicago Police and Cook County Sheriff have their own training facility.
Since educational records can not be released, I doubt they would give you any information.

I wish I could give you some good news, but it is not promising. Good Luck with your search.

George Lynn Boise
lboise@insightbb.com