The following is a useful summary, found at “Nudity and Public Decency Laws in America” (by hg.org):
Generally, in America, nudity is against the law in public places. Moreover, nudity is also generally illegal on a person’s own property if the nude person is visible to the public, such as through an open window or sunbathing nude in someone's yard. While most state laws are clear about nudity around children and nudity meant to arouse, some other wording is vague and violations often are a matter of community standards for indecency. Of course, in some situations, these laws may conflict with constitutional protections for freedom of expression, particularly if the nudity is part of an artistic performance or political demonstration.
There are no federal laws either for or against nudity, except to the extent that it may be protected under the First Amendment right to freedom of expression. Local laws will take precedence when the question of nudity relates to federal lands, such as federal parks, beaches, and other facilities.
In some states there are public lands where nudity is allowed or simply tolerated. There are also private facilities where nudity is allowed in almost every state, with the usual requirement being that the nudity must simply not be observable from outside, public areas.
New York, Hawaii, Maine, Ohio, and Texas are unique in that they each have laws expressly allowing women to go topless in any location where men could do so legally."
The only state with a generally tolerant attitude toward public nudity is Vermont. There is no state-wide prohibition on simple public nudity, but at least six municipalities have ordinances against it. Of course, other laws about public disturbances can be invoked if the public nudity is perceived to be causing a problem, and the naturist should use careful discretion even in Vermont.
The federal system of government in the United States creates a level of complexity that makes it confusing to discern what the law is in any particular location. State criminal laws, county ordinances, city ordinances, and agency regulations (such as in state parks) may all apply. Enforcement can be uneven; in many cases laws against public lewdness are invoked to bring charges for simple nudity. Depending on the jurisdiction, penalties can range from a small fine to years in prison and permanent inclusion on a sexual offenders registry that includes rapists and perpetrators of sexual abuse. It is essential for a naturist who is contemplating being nude outside the confines of a nudist resort to know the locally applicable laws and practices and the potential penalties for contravening those laws and practices.
The best source for the naturist is the list of state laws maintained by the Naturist Action Committee at “State Laws” (naturistaction.org).
– Written by: Milt, USA