"As of April 15, 2016, Alaska, Arizona, Arkansas[disputed], Idaho (residents only), Kansas, Maine, Mississippi, Puerto Rico[disputed], Vermont, West Virginia and Wyoming (residents only) do not require a permit to carry a concealed firearm for any person of age (usually 21 and older) who is not prohibited from owning a firearm. Permitless carry in Idaho and Wyoming is applicable to residents only; non-residents must have a permit to carry a concealed handgun in these states. All aforementioned jurisdictions do not require a permit to openly carry either."
*Arkansas is not really a Constitutional Carry state, since in the state only open carry is legal without a license.
"In the state of Oklahoma, any person who is a legal resident of a state that allows concealed carry without a permit may also carry concealed in Oklahoma without a permit, so long as they possess a photo ID showing they are a legal resident of that other state and also meet the legal requirements for permitless carry in that other state."