The place to begin when looking for online gambling sites legal for residents of where you live. From here we link to the legal gambling guides for all states.
There is no U.S. federal law against gambling online. On the federal level, gambling online is perfectly legal, because of the lack of a law against it. It's possible.
The fact that a state has not passed a specific law does not make participation in or offering of gambling over the Internet legal under the laws of that state.