While 18 is typically the minimum age for marriage in the United States, every state has legal loopholes or exceptions allowing children to wed at a younger age.
This is historic," Fraidy Reiss, founder of Unchained at Last, a non-profit group opposed to child marriage, told the Thomson Reuters Foundation.
Globally 12 million girls are married before 18 every year, according to Girls Not Brides, a partnership of organizations working to end child marriage.
The measure banning marriage for anyone under 18 passed Delaware's Senate unanimously last week after passing the state House of Representatives in April.
Lawmakers in Florida recently considered a bill to ban marriage for anyone under 18 but compromised on a law banning marriage under 17.
A bill to end child marriage in New Jersey is moving through the legislature where it is expected to be approved.
"I'm just hoping that Delaware won't remain the only state to pass this," Rep. Kim Williams, a Democrat who sponsored the legislation, told the Thomson Reuters Foundation. »