Katanas fall under the category of knives and are regulated as such by state laws, making their ownership perfectly legal. In the United States, individuals must be either 18 years old or have explicit parental consent to possess a Katana.
The ability to carry a Katana outdoors varies by state, and we advise you to personally verify the laws in your specific state. As a general rule, openly carrying the sword in public is prohibited, and it should be securely stored in a designated bag or case.