This is a question for state law. State nonprofit corporation statutes anticipate that there will be bylaws—but I am not sure that all states  actually require bylaws. In many states, the statutes provide basic procedural rules for governing the organization in the absence of bylaw provisions to the contrary.

But it clearly makes sense to establish your own rules of governance in bylaws and have them readily available for everyone to review. It is particularly important in those states where you must put limitations on director liability and provisions for indemnification in the bylaws if you want to avail yourself of the protections. You may be interested in our Ready Reference Page "Bylaws Function as “Constitution” Of Nonprofit Corporations."

For more information on nonprofit bylaws consider listening to one of our pre-recorded webinars in our Store - Bylaws: The "Constitution" of Nonprofits - The Art and Science of Making Them Work.