The source is the legal code which you can look up on dozens of sites like this one.

https://statelaws.findlaw.com

California and Wyoming are the same — all require court approval.

I think you should consider that the mentality of people living 100 or even 50 years ago was not the same as it is now. The rules of decent behavior were determined by chrisitan society and not lawyers. The need for lawyers to settle disputes was rare. That was up to ministers and priests. The church did not allow babies to marry. All judges on the bench were christians in good standing with the church. All.

Any judge that gave permission for someone to marry a baby would have been removed from the bench or perhaps just strung from a tree. And no one would have batted an eye. Because everyone agreed that christian morality trumped legal rulings. You know nothing of this because you have grown up in a litigeous society. Most people think law is the basis of right and wrong in the US. But people in the past believed that leaving rare complex cases to the best judgement of a respected member of society was more sensible than trying to account for every eventuality.

The idea that every eventuality must be written into legal code because if legal code does not bar a behavior it is acceptable is not an idea that comes from European christian culture or English Common Law, it comes from Talmudic scholarship— i.e. If the bible doesnt ban it, you can do it. That is the principle on which this country is run today. But not historically.

Child brides were rare in the past because monogamy was enforced and people were not allowed to have sex out of wedlock. It was a crime and a sin. Northwest europeans all practiced enforced monogamy, a system that drives up the marriage age, genetically as I have explained elsewhere. The average age of marriage for females in northwest Europe has been 23 for about 800 years at least. Pagan Germanic hoards had a marriage age limit at 20 per Tacitus. Brides younger than 15 were so rare as to not be worth mentioning. Basically these young marriages only happened among the aristocracy.

So when marriage of a child bride occured in the US it was historically only because someone had already had sex illegally out of wedlock with a young person and they may have been pregnant and their reputation for not being the town whore for the rest of their life was in jeopardy. And perhaps they felt the childs immortal soul was in danger as well.

Generally very young people like this did not have decent parents looking after them and marriage was one way to ensure that they were fed and there was a roof over their heads. There was no such thing as welfare of public housing. Facilities for wayward women was shit. For many, marriage was the best slice of a shit pie.

Being the town whore was a life ruiner because everyone understood the danger of the end of monogamy. Look around.

You may not feel like it is reasonable for people to brand someone a whore for getting knocked up at 12 out of wedlock but enforced monogamy is a package, when you turn it in to a buffet it falls apart. Enforced monogamy is a system that worked for thousands of years in Europe, it keeps marriage age of females high, rate of paternal responsibility high, and a whole bunch of things we take for granted that will start to fade, now that we are a POLYGAMOUS society. Keeping out of wedlock sex and bastardy taboo worked to discourage people from fucking recklessly.

Monogamy has the best record for minors not getting FUCKED. Our society has destroyed all the barriers to prevent minors from getting fucked. Litigeousness is destroying our cultural values. Secularism has destroyed monogamy. And now we are importing people from populations in which child brides are typical, not rare— populations in which sex with very young females is a genetic predisposition because of polygamy.

You are taking some laws totally out of context because you think the world a hundred years ago is the same as it is now. There was an entire set of cultural and religious rules that modern America has thrown out. All these people fighting for sexual access to young children would have been jailed or killed. Problem solved. You think the solution to the problem is more laws and more lawyers. It isn’t. Secular rule is the problem.