14-year-olds can legally marry in the U.S.?!

As I’m reading about the background of John Karr, I read that he was married before: once to a 16-year old and once before to a 14 year old.

As someone who has always understood that 18 was the age a person is a legal adult in this country (though I’ve heard that "age of consent in some places is 16?). How does a 14-year old get married?

It used to be common for a rural family to marry off their 15-yo daughter to a 20-yo or so man in the community.
In 1905, a housewife or farm wife would know all she needed to known about housewifing or farm wifing by the time she was 15, and when you’re dirt poor it is attractive to have one less mouth at home to feed.
The parents of at least two of my grandparents more or less fit the description above… that would mean it wasn’t too uncommon in Appalachia in the 1910-1920 era.
What you’re seeing is laws that haven’t been updated yet to reflect changing customs.

Here is a list of age laws in the United States. It looks like all states allow marriage under the age of 18, most of the time with parental and/or court consent.

Marriage is considered automatic legal consent in every state. Girls can get married as young as age 12 with a judge’s approval in some states at some times. Presumably, the rationale behind this was to make babies legitimate after their conception but before birth.

There is a chart of ages for all 50 states here.

And as Wikipedia says, The age of consent “should not be confused with the age of majority or age of criminal responsibility or the marriageable age.”

If you’re wondering how a girl can give informed consent to a supposedly permanent marriage to and a lifetime of sex with a man of any age at 12, but can’t give informed consent to a single sex act with her same-age boyfriend even if she is several years older than that, well, that would make for a good GD thread.