Originally Posted by twinboat
A CDL is a " Commercial Drivers License ". Unless your driving for money, it won't be needed anywhere.
This is the answer in a nutshell.
As others have said, the operative word is "commercial" pertaining to a CDL.
However, in a lot of states, you may be required to be tested for and to acquire a special license to operate a tractor and a 5th-wheel. A "tractor" doesn't necessarily have to be a Class 8 tractor, it can be a one-ton pickup when pertaining to a special license needing to be required.
In Nevada for instance, you'd need a non-commercial Class A license or a Class C license with a "J" endorsement. It will depend on the weights of the tractor and the trailer as to which you'd need.
Attached is each state's requirements for their own residents (the state in which you hold your driver's license but as has been mentioned, as long as you are correctly licensed in your own state, reciprocity among states will allow you to operate in any state) ...not sure how up to date it is now but be sure to check with your state for the current laws.