It does NOT make a lick of difference if it is a 'law' or not in that particular state.
The law pertains to the highways that are patrolled by police and WILL enforce the 'law'.
CG's are private property just as your own property.
If your state has a helmet law? You most definitely can ride on your own property with OUT a helmet.
Countless stories of kids riding big 4 wheelers and crashing with out a helmet in states that have a helmet law. They are not issued a ticket.
Albeit many of them do die from head injuries.:(
Just wish there was this much interest about following the CG rule of no loose dogs!