What can I do to find out what happen to savings after bank folded.

This is a fun answer for me at least. Illinois has a website through the treasurer's office that is provided in the link below. Without more information I cannot tell you if the bank was insured or if this was the type of account that would be given insurance through the federal government. I can tell you that in 1983 the FDIC stopped giving refunds until Congress refunded the program I do not know if there is a look back period for a bank that folded in the 1970s. Cash dash through the Illinois government provides a way in which people can find forgotten funds at various institutions. Simply put in your name and possible matches will come up. I can tell you from personal experience that this is easy and requires just a few minutes of your time. Last summer my wife went to the site and found we were owed $90 from an account closed 15 years ago. Have fun if you have any questions do not hesitate to contact my office.
Unfortunately, in the small space provided for questions one is unable to get a full background of the matter. In the situations such as you are explaining you should immediately seek the counsel of a capable attorney that practices in this area of law or if you cannot afford an attorney, you should seek a social service organization in your area. This answer is general in nature and does not form an attorney client relationship. If you would like to get more information on this topic or to establish an attorney client relationship please contacts my office.
This may be deemed an advertisement and as such: information contained within this answer has been approved by Bradley L. Schencker, a licensed attorney to practice law in the State of Illinois, for any questions contact Bradley L. Schencker by the methods provided herein.