From the www:

'"You may have heard that Nevada is the only state in the USA where prostitution is legal. That is correct; but prostitution is not legal everywhere in Nevada, and it is not legal in Las Vegas. That's right! Prostitution is illegal in sin city. It is only legal in certain counties that have chosen to make it legal. Clark County Nevada and its principal city Las Vegas chose to not make prostitution legal. It is also illegal in Henderson, Laughlin and Boulder City.'