There are no restrictions if you are coming in or going out of the United States, but you must declare your cash you have to the CBP if it exceeds $10,000.
Why Your Travel Destination May Be Important
Single Market Economy reports that Canada and Mexico are the top destinations for US resident travelers, followed by the United Kingdom, Italy, and France.
When you arrive at the airport, you may have to fill out a customs declaration form on which you are expected to divulge how much cash you are flying with.
Safety Concerns When Flying With Cash Into A New Country
A money belt or a hidden pocket can be a secure space; you may also split your cash if you carry large amounts.
Remember, the legality of the cash you carry does not guarantee its safety, so you must use secure ways to protect your cash against theft and fleecing.