Fwiw ORD was easy to schedule. By easy I mean there is a lot of availability even a few days before wanting to schedule.

I found other locations in the midwest very difficult. For example, Cincinnati & St. Louis were weeks (if not months) out.

My wife scheduled a week or so ago for Peoria (there was a slot for early May), but we happened to check Indianapolis yesterday morning about 5 am. Unbelievable (to me) and there was one slot available - she was able to get in yesterday. CBP was doing a "mobile enrollment" there. The next available dates are May 3-4. The office they used was located on the baggage claim level in the back next to the United baggage claim office - between baggage claim 1 & 2. If you are near Indy, keep checking every day, including the day of the event. You might be able to do a walk in. We got there about 45 min early (no one else waiting) and she was interviewed within a few minutes. Very laid back. Great officers.

CBP Global Entry Mobile Enrollment Coming to Indianapolis International Airport