According to OpenCarry.org (https://opencarry.org)
In 30 of the 50 U.S. states, you can legally carry around a gun with no permit.
In 15 of the 50 U.S. states, you can legally carry around a gun as long as you have a permit.
In 5 of the 50 U.S. states, you cannot legally carry around a gun**
**One of the “No Open Carry Permitted” states — California — allows citizens to carry a loaded and exposed (not hidden) gun with a permit if they live in a county that has fewer than 200,000 people. 30 out of 58 of California’s counties have fewer than 200,000 people, meaning that 2,077,850 California residents (5% of the state’s total population) are legally allowed to carry arms — assuming they are not parolees or mentally ill.