Child brides in the US share stories of exploitation, becoming a wife: 'I knew I was 11. I knew he was 20.' "Everything changed. I wasn't me anymore."

They're portrayed as modern-day Romeos and Juliets -- young, star-crossed lovers in dramas like "The Secret Life of the American Teenager" and reality shows like "Say Yes to the Dress."

But for hundreds of thousands of young girls across America, their wedding's a far cry from happily ever after.

Child marriage is an issue many can't imagine would exist in America.

But over the course of a year-long investigation, "Nightline" traveled from the East Coast to the mountainous west to the heartland, uncovering America's child brides.

For Ashley Duncan, what started as a typical school day as a freshman in high school ended with her becoming a wife.

"My aunt, she got on the bus not long after I did and said, 'Come on get off the bus, you're going to get married,'" Duncan remembered. She was 15 years old.

After discovering she was pregnant, Duncan believed marrying her 18-year-old boyfriend was her only option. She said no one asked her anything at the courthouse or confirmed with her if she was sure about getting married.

"I was scared but, at the time I was told and believed," She said. "I found out it's not true ... that since he was 18 or older he would go to jail because I was pregnant."

She said she didn't realize how big of a commitment she was making. She had dreams about what her wedding day would be like.

"My dress. I've always wanted [it] to be different," she said. "A traditional wedding is the bride wears white and the husband wears like a black tuxedo or something. And I wanted to wear a black dress and I wanted the men to wear white."

On the day Duncan was married, she remembered she "was wearing just regular pants … and my hoodie," not the dress she dreamed of.

The numbers show that Duncan's story is far from unique -- a report by the Tahirih Justice Center, a non-profit that provides legal and social services to immigrant women and children and aims to protect them from violence, revealed that between 2000 and 2015, over 200,000 children were married in America.

And it's legal. Almost every state in the U.S. allows child marriage with exceptions. In many instances, all you need is the approval of a judge, a clerk or a parent.

In 13 states, there is no minimum age.

Duncan said it was "hard" going back to school. "I wasn't the same going back as it was the day I got on the bus."

"Everything changed, I wasn't me anymore," she said. "I had a whole different last name. My teachers were getting confused -- kids really picking at me because my name was different and I was too young to be married."

She went to school that day as Ashley Tidwell. The next day, she was Ashley Duncan.

Soon enough, Duncan dropped out of school, and after two years of marriage and the birth of her second child, she and her husband separated.

Even though Duncan and her husband were both teens, the vast majority of marriages occur between an adult man and a much younger girl, some as young as 11.

That's how old Sherry Johnson was when she got married to a man nearly twice her age.

"We got married that night after church," she remembered. "Nobody said anything. I knew I was a child. I knew I was 11. I knew he was 20. So I knew something was wrong then. And I was really totally surprised that they allowed it to happen."

Johnson, now 59, said she was forced into the responsibilities of marriage by her parents. Her husband, a deacon in the church, had statutorily raped her prior to their marriage.

"I was being raped by people with authority," she said. "I didn't know what was actually really happening. I just know that something wasn't right about it."

She had already given birth to their first child at just age 10. Soon, she was pregnant again.

"I remember going to school at the time, in the fifth grade ... coming home and [I] had to wash diapers out in the tub," she said.

Like so many child brides, she dropped out of school.

Over their seven years of marriage, she would have six children. She finally left her husband when she turned 17 and later divorced him.

The effects of these unions can be devastating. Now she is fighting to end child marriage in Florida. Last year, her story was read into the record of the Florida Senate. Just before lawmakers passed a bill to raise the minimum age of marriage in the state of Florida to 17 years of age.

"Ms. Johnson is the reason for this bill," said Florida State Senator Lizbeth Benacquisto (R) during her remarks on the floor, stating, "Ms. Johnson was raped at a very young age by her deacon at her church. And when it was found out that she was pregnant, her parents, her parents did the unthinkable they forced her to marry the man who impregnated her as a child."

Jeanne Smoot, senior counsel for policy and strategy at the Tahirih Justice Center said, "There is obvious potential for abuse and exploitation...a whole host of horrors to lurk behind a marriage license that involves a child."

"There is just far greater vulnerability to domestic violence and further exploitation if you marry underage," she continued. "So, we know that women who marry underage, face higher dropout rates from school, [there's a] much greater likelihood of future poverty. They face more medical and mental health problems. They face high divorce rates."

Smoot said the rate of domestic abuse is three times higher for child brides and they are twice as likely to end up in poverty and drop out of school.

These marriages can also serve as a legal loophole for men to skirt statutory rape charges, she added.

"You can be married younger than you can legally consent to sex," Smoot said. "So you put all of this together and you've effectively road mapped a way that predators can find a work-around through a marriage to gain sexual access to young girls that would otherwise be prohibited."

The laws are moving some to take action. Fraidy Reiss is the head of Unchained At Last, a nonprofit advocacy group that works to end forced and child marriages throughout the country. She has protested child marriage laws in various states including New Jersey, where former Gov. Chris Christie vetoed a law in 2017 that would raise the minimum age of marriage to 18. At the time, he justified the decision by saying that a total ban on minor marriages would violate the culture and traditions of some communities.

A year later, current New Jersey Gov. Patrick Murphy signed a law that set the minimum age for marriage in the state at age 18.

Reiss runs Unchained At Last out of an office that she says is in an undisclosed location to protect those who are trying to escape. She said the phone rings all day with calls for help, but that oftentimes they are unable to provide it.

"When a child reaches out to us and says, 'Please help me. I'm about to be forced into a marriage' or 'I was just forced into a marriage,' there's almost nothing that we can do to help her," Reiss said. "We could be charged with kidnapping if we help her to leave home. It's heartbreaking for me."

But not all girls who get married as children seek help, and with state laws slow to change some schools have adopted curriculums that teach them how to navigate marriage in healthier ways.

At Triumph High School, an alternative high school in Cheyenne, Wyoming, Dr. Michelle Aldrich is among other teachers who educate their students about co-parenting, handing each other's emotions and divorce, among other issues married couples encounter.

"My first piece of advice is always, 'So tell me why this is the one -- why is this the one?'" Aldrich said. "You know, is it because it's a way out? A way to get away from your home life or your parents? Is it because you are just madly in love? Why is this the one and how do you know? And I think that a lot of times [it's] telling."

When asked about their reasons for choosing to get married, Aldrich said, "I think a lot of times it's parental pressure."

After Abby Gillis, who graduated from Triumph last year, found out she was pregnant at age 16 by her 20-year-old boyfriend, Ezra Gillis, she said she knew she wanted to marry him. She said her decision to get married was by choice, making her an exception -- no one forced her into it. Ezra Gillis said that they decided to get married because they had been "best friends" for "quite some time."

Abby Gillis' mother, Victoria Lynn Sopr, said she cried on their wedding day.

"Nobody wants to see their 16-year-old get married," Sopr said. "So I cried. ... I had like a whole lot of emotions that day. You know, part of me was, 'Am I sure that this is the life that I want her to lead?' and then the other part is you want her to be successful. You want this baby to have a dad, you want all of these things."

"I was also a little bit worried because, her being 16, I wasn't sure if she was mature enough to handle all of the things that come with marriage and children and everything," Sopr added.

Abby Gillis, now 19, admitted that she had to grow up fast. She said her life might have been a lot different had she not gotten pregnant and that having a baby was "God's way of telling me to 'wake up, it's time to be an adult.'"

Sopr said she saw a noticeable difference once she got married, even making honor roll at her high school.

"Her dad and I went to parent-teacher conferences and every one of her teachers said, 'I cannot believe how mature Abby is,'" Sopr said. "Her dad and I both looked at each other and we were like, 'Are they talking about our kid?' There's no way that this is happening."

Abby Gillis expressed support for any girl who wishes to get married before 18, and said that she would be "disappointed" if that law was changed.

"I think there is no age limitation when it comes to love," Abby Gillis said. "I think that you know who you love -- when they uplift you and your face just lights up and you feel like their heart skips a beat or you just get butterflies because the presence is there. And I think that people would say that's puppy love, but puppy love is still love."

"I think some people want the security," she continued. "For me, the security of having him til' death do we part. That's the thing I think of every day. I made that vow to him."

But many cautioned against that logic.

"Some people say well there shouldn't be an age limit on love if you're 16 or 17 and you're in love with your 18-year-old boyfriend why should you be allowed to get married? Well, nobody's putting an age limit on love. We're putting an age limit on marriage," Reiss said.

Last year, child marriages were been banned in two states: Delaware and New Jersey. But some others have made incremental changes in an effort to better protect young women. In Missouri, for example, the minimum age to marry was raised from 15 to 16 after Duncan came forward with her story.

"It should definitely be harder for 15-, 14-, 13-year-olds to get married, it should definitely be harder," she said.

It's a desire that her aunt, Christina Cothran, shared as well. She told "Nightline" she regrets her decision to sign for Duncan's marriage when she was so young and said she too was married at age 15. She said it is time for the laws to change.

"I believe, she's not always had the best judgment," Duncan said of her aunt. "When I was a kid, a kid um, our relationship was really good um, she was like my favorite person and life got hard for us and for her, I'm not going to go into detail but, I love her."

Now 26 years old and with two more sons, Duncan has a fiancé who she wants to marry. However, she is unable to pay for a divorce to the man she married 10 years ago. After living through her own child marriage, she offered up some advice for young teenage girls who find themselves in the same situation.

"You have a whole life ahead of you, and it's not how you want to do it," she said. "If you are in a relationship that you think is going to last forever, you can at least wait until you are old enough to not have a legal parent or guardian sign your marriage license for you to marry."