You simply need to be located in the state at the time you place a bet. DraftKings is also legal for Daily Fantasy Sports (DFS) in all but six U.S. states -- Hawaii, Idaho, Montana, Nevada, Oregon, and Washington.
The states where DraftKings is illegal to use include Alabama, Alaska, California, Florida, Georgia, Kentucky, Massachusetts, Minnesota, Missouri, New Mexico, North Dakota, Oklahoma, South Carolina, Texas, Utah, Vermont, and Wisconsin. California and Florida are both up for consideration to allow gambling.