Most county jails don't do any identity checks as they release detainees (except ask their ID number and birth date), they are usually small enough for the staff to know all the prisoners.
I remember one incident at the Cook County Jail where two prisoners "swapped identity":
https://www.cbsnews.com/chicago/news/escaped-inmate-jahquez-...
That looks like a case where the normal identity checks weren't done:
>> Scott donned a medical mask and posed as Henderson, using his name and personal information to leave the jail, according to the sheriff's office.