The Insurance Institute for Highway Safety, Highway Loss Data Institute maintains a list of Helmet Use Laws for motocycles and bicycles by US state. Whether unicycles count as bicycles in your state is not included, but the list can still be a handy guide.
Cheers,
Raphael Lasar
Matawan, NJ
That page doesn’t list any of the local city our county laws that require bicycle helmet use. For example, King County and the city of Seattle now have a bicycle helmet law that covers all riders (minors and adults). Just because there is no statewide bicycle helmet law doesn’t mean that local cities or counties haven’t enacted such a law.