A religious marriage has no legal standing in U.S. civil law. A clergyman may perform a religious marriage anywhere in the United States without any registration and without the couple ever registering a civil marriage. It will be considered as if they are not married, under civil law. The couple will be, according to civil law, two unrelated people. And that arrangement is entirely legal. The Constitution generally prohibits the State from regulating a religious function. In this case described, the religious marriage is a religious function.
If the State is one of the ten “common-law marriage” States, the couple will be considered married (by virtue of their living arangements; not by virtue of their religious ceremony.) In the other 40 States, they will be considered unmarried. There is no law anywhere in the U.S. (anymore) prohibiting two unmarried people from living together and having children. In fact, such unmarried arrangements is quite common these days (and entirely legal) among the secular American populace.
The Fundamentalist Mormons, even today, perform religious marriage ceremonies between one man and multiple wives. As long as they do not register a second wife as a civil marriage, they are not prosecuted for bigamy notwithstanding the fact they are religiously married to more than one wife. (Think about it: If it were illegal for a clergyman to perform a religious marriage without a civil marriage, what exactly would they charge the couple or the clergyman with? Nothing. And that is even where there is only one husband and one wife! They don’t charge even if he is marrying a guy to two wives..)
truthsharer: Please clarify your point about how and why Florida is different in regards to “second marriages”. Are you referring to bigamy?