porn laws are not determined by county. they are determined by case law. theres a case out of the LA civil appeals court that states paying someone to have sex on film with someone else isnt pandering or prostitution. This might not be applicable to movies were the producer and talent are one in the same.I dont know of any other jurisdiction were filming adult content is legal.
before you consider filming content, get a lawyer that knows the business side of this, not just 1st Amendment issues. if you are going to shoot in LA, there are so many issues you have to be aware of. its easy to make a mistake that can be quite serious legally.
Michael