We are not aware of any specific law that makes it illegal for you to keep a hitch with a ball on your vehicle when it is not in use however state laws vary and are updated regularly so there may be some states that have statutes stating that a trailer hitch ball must be taken off when it is not in use.
We have read is that in some states where there is not a state law regarding ball hitches there are some city ordinances that require you to take off the hitch ball when it is not in use or that local jurisdiction will cite you for it.
In most states there are laws that require your license plate to be able to be seen in full and we have seen motorists that are ticketed when their trailer hitch is obscuring the view of their license plate. In these cases the law is not specifically against having a ball hitch on your vehicle when it is not in use but allows officers to ticket you for a ball hitch covering part of your license plate which is against the law.
To find out if your state has a law requires a trailer hitch with a ball to be removed when it is not in use contact your state's Department of Motor Vehicles and/or the state police. Either should be able to tell you if there is a specific law surrounding a ball hitch in your area.
We have read that in the state of Illinois they have tried to pass a law regarding ball hitches but to the best of our knowledge it has not passed and become a law as of yet. In 2009 it was purposed that the Illinois Compiled Statutes (ILCS) should be amended to add a law about ball hitches under the motor vehicle equipment section (625 ILCS 5/12-614 specifically).
IL House Bill 3669 in 2009 was filed to amend the Illinois Vehicle Code and it stated "so that if any portion of a motor vehicle hitch containing a ball mount and receiver extends more than 4" beyond the vehicle's rear bumper, then the ball mount must be removed from the hitch receiver when not being used for towing. If any portion of the hitch extends beyond the 4" of the bumper and is composed of a single assembly that cannot be removed from the vehicle, then the ball of the hitch must be covered with a RED cover." The bill was referred to the rules committee last we heard but in the future this could push forward and make it illegal in Illinois to keep the ball hitch on if not in use or if it is not removable it would have to be covered.
Again to find out if your state's laws require a ball hitch must be removed if it is not in use, contact the state police who would know if they ticket anyone for this type of offense and/or the DMV.
Get inexpensive car insurance quotes here.