As of the time of writing this page, the following states have already legalized sports betting: Oregon, Delaware, Nevada, Arkansas, Illinois, Michigan, Monatana, New Jersey, New York, Mississippi, West Virginia, Washington, D.C., Colorado, New Mexico, Pennsylvania, Iowa, Rhode Island, New Hampshire, Indiana, and North Carolina. It means that you may bet in these states.
Nevertheless, be sure to stick to the local betting laws, as they vary from state to state. In addition, be advised to check the taxation laws in order not to break the law and get into illegal betting. The number and kinds of sports to bet on also differ in each of the states listed above.