<p>No one said anything about the OP or anyone else being a criminal (although starting a thread title with “How do I keep my money hidden…” may be an unfortunate choice of words). In the post 9/11 banking environment financial institutions have staff who are trained to watch for anomolous behavior and also have technology that tracks it. In some situations there is a legal requirement to report same to federal law enforcement authorities. It’s a far more productive idea to put money into savings, or some interest bearing account, for several reasons. It’s not illegal to keep money in jars, under mattresses, in shoe boxes, or, like the OP, even in safe deposit boxes, as a matter of personal preference. It may be illegal to do so in an effort to avoid detection for further economic gain.</p>