How long do you need to keep records for closed trust accounts? I've seen information indicating "forever" and other information that indicates for only ten years.

It depends largely on your state laws and of course what types of records you are talking about.

The best resource to start may be with you State Banking Association. Chances they may have a records retention manual available for purchase that is specific to your state and is comprehensive and specific to the banking industry. I know ours does.