Only illegal because they'd have to be stolen. Unlike the 500/1000/5000/10000 notes the $100,000 notes were never issued to the public. They were a relic of the days of physical currency transfer between banks.
Not that many 500/1000/5000/10000 notes were used in practice either. Less than a thousand of the big ones and a few hundred thousand of the "smaller" ones even exist. They're all in collections now as the Fed requires banks to return them for shredding if deposited. Collectors will pay a lot more than face value for them so you'd be nuts to try to spend one.
Not that many 500/1000/5000/10000 notes were used in practice either. Less than a thousand of the big ones and a few hundred thousand of the "smaller" ones even exist. They're all in collections now as the Fed requires banks to return them for shredding if deposited. Collectors will pay a lot more than face value for them so you'd be nuts to try to spend one.