Police said the teen also shot a 31-year-old man in the same incident. He is facing two felony counts of attempted first-degree murder and two felony counts of aggravated battery/discharge of a firearm.
The teen was arrested in the 3300-block of West Ogden Avenue shortly before 1:30 p.m. Friday. Police said this is the teen's first arrest.
The little girl wearing a Minnie Mouse costume was shot in the neck and chest by stray bullets in the 3700 block of West 26th Street at about 5:30 p.m., officials said. She was among several children trick-or-treating at local businesses when someone opened fire at rival gang members.
A 31-year-old man who is not related to the girl was shot in the hand.
The shooter wore a mask like the one worn by Jason in the movie "Friday the 13th," Superintendent Eddie Johnson said at a press conference Friday morning.
"The shooting yesterday was reprehensible and those involved don't deserve to be in our city," Johnson said. "I am disgusted but committed to doing everything we can to finding the cowards that would engage in a gun battle in the early evening hours while children were trick-or-treating."
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The girl remains in critical, but stable condition at Stroger Hospital.
The man was transported to Mount Sinai Hospital in stable condition.
Chicago police said the gunman was likely targeting the man who was shot in the hand.
Families ran into nearby stores to get away from the gunfire.
The girl's father rushed her into a nearby cellphone store, where a worker applied pressure to her wounds.
"This is a crime that touches all of us," Superintendent Johnson said. "There is no place for this savagery in our city."
Johnson said the response from the Little Village community has been overwhelming as residents have passed on information to police. Police were able to pull some surveillance video from nearby businesses.
Neighbors near the scene of the shooting are expressing anger and defiance on Friday.
"We are here to show our support and show our prayers for this little girl and her family, and we're also here to show our outrage," said Little Village native Peter Garza.
"It is unacceptable a 7-year-old girl that is trick-or-treating with her family out here and happens to get shot," said Sgt. Rocco Alioto, Chicago Police Department. "Because a group of guys wanted to shoot at another male while there's a street full of kids trick-or-treating."
Anna Dickey didn't take her children out trick or treating in the neighborhood Thursday night.
"Me and my husband talked about it this year and I was like, 'We're not gonna take 'em out,'" Dickey said.
Dickey said she made the decision considering both the cold weather and safety concerns.
"Our kids can't enjoy the things that we used to," she said.
Others are scared too.
"I hear it from the older folks too like my dad," Ivonne Chavez. "They've been here way longer than I have and they're scared. We're scared to go and walk to the local corner store."