Is it breaking the law to ride your motor bike in the US without wearing helmet?

It depends on the State / City laws. Most states require helmets for people under 18, but very few require helmets for adults.

It's a state by state decision. Some states yes, some no.

America is SUPPOSED to be dominated by individual rights and then states rights. Unfortunately, every year liberals take more and more rights away from the individual and the states and gives them to the federal government.

Don't be surprised if we enact a nation wide helmet law completely unconstitutionally one day.

See map link below.

It's up to each state.

Of the fifty states, only 4 are 100% helmet law free!

Colorado, Illinois, Iowa and New Hampshire

19 States have helmet laws that exempt adult riders, riders over the age of majority -- 18 years old and over. Those states are:
Alaska, Arizona, Connecticut, Delaware, Hawaii, Idaho, Indiana, Kansas, Maine, Minnesota, Montana, New Mexico, North Dakota, Ohio, Oklahoma, South Dakota, Utah, Wisconsin and Wyoming.

There are 7 states that discriminate against adult bikers between the ages of 18 and 20. How bikers ever got involved in discriminating against their own kind (just younger) is beyond our comprehension. Those embarassments to the community are:

Arkansas, Florida, Kentucky , Pennsylvania, Rhode Island, South Carolina, and Texas.

"In the US", no - there is no Federal law on the subject.

In "most" States, however, it's illegal, but in some it isn't.

This is a matter for State law, not national law.

Richard

Depends on the state. Some states mandate wearing helmets. Some don't. Just know the law before you cross state lines.