Sweepstakes casinos are legal in most states. The only state that forbids sweepstakes play is Washington, and in Idaho you can play but cash prizes are illegal.
Note that while Michigan has not banned sweeps casinos, major operators like Chumba and WOW Vegas are no longer available.
You can claim sweepstakes no deposit bonuses in all states that allow sweepstakes casinos to operate, including California, Texas, Florida, and New York.