Survivors of gun violence in a club no one asked to join

Lindsey Hartman, one of the survivors of the Highland Park shooting that unfolded on July 4, said although her and her family escaped physically unharmed, they remain mentally scarred.

"It just doesn't go away just because the camera crews and the headlines go away," she told "Nightline" co-anchor Byron Pitts. "I mean, it's something that sticks with you forever."

The shooting, during which a gunman opened fire during a 4th of July parade in the Chicago suburb, killed seven people and injured 48.

"It's still pretty raw, you know. There's a lot of emotions that are still very much at the surface," she said. "Fear. Gratitude. Terror."

The mass shooting that Hartman and her family survived at Highland Park is one the more than 600 mass shootings that have unfolded in the U.S. this year, according to the Gun Violence Archive.

In the U.S., more than 115,000 people are shot by a gun every year and in the past 30 years, gun violence has claimed more than a million lives.

Yet this number just scratches the surface of the people affected by gun violence, not encompassing people that have survived injuries, witnessed gun violence or seen it impact family members.

On average, more than 100 people die each day from gun violence yet more than 200 people sustain a nonfatal injury, according to data analyzed by Everytown for Gun Safety.

Hartman is part of the Everytown Survivor Network, a community of people that have survived gun violence who support each other and engage in advocacy. Through the program, she met fellow Chicago-resident and survivor, Valerie Burgest.

Burgest's son Craig was shot and killed in 2013 while he was buying gum in a convenience store. He was 23 years old. The case remains unsolved.

The relationships she has formed through the Everytown Survivor Network are "powerful," Burgest said, "because you really don't have to explain yourself."

"Val buried a son," Hartman said. "And that is unimaginable. That is the worst kind of pain for any parent. But she never looks at me and says, 'Your pain is less.'"

Another relationship, between Pastor Jackie Jackson and Doreen Dodgen-Magee illustrates the strength of bonds between survivors.

Jackson and Dodgen-Magee met four years ago through the Survivor Network and have become very close ever since.

"I took some food off of Jackie's plate when we were at a meeting together," Dodgen-Magee said.

"She just reached over. No conversation," Jackson said. "I said, 'Hold up. You got to be my family to take food off my plate.' And she said, 'Well, I guess we'll just have to adopt each other.'"

"And we did," Dodgen-Magee said.

Spending time together has been an important part of her growth, Dodgen-Magee said, just "being able to have fun."

"It is so important because the world is so heavy when this is your reality," she added.

"We managed to find space in this club for each other and ourselves," said another survivor, Brenda Mitchell.

"Everytown Survivor Network, and I say this unequivocally, saved my life," she said.