It's not illegal to store cash in a safe deposit box, but some banks have policies which will state that you cannot. Ostensibly over money laundering / illegal

It's not illegal to store cash in a safe deposit box, but some banks have policies which will state that you cannot. Ostensibly over money laundering / illegal asset hiding concerns. But regardless of policy, it really does not make a whole lot of sense to keep your cash in there. If you just deposit the cash at the counter it's insured through FDIC, in the box it's not.