According to Unchained At Last, a nonprofit "dedicated to helping women leave arranged and forced marriages," only six states prohibit marriage prior to age 18: New York, New Jersey, Delaware, Rhode Island, Pennsylvania and Minnesota.
Among the remaining states:
In most cases, these states require parental and/or judicial consent for underage marriage.
Unchained At Last reported in 2021 that 300,000 minors were legally married in the U.S. between 2000 and 2018. Ninety six percent were age 16 or older, while less than 1% were 14 or younger.