A man driving to work just after 4 a.m. saw the girl standing by herself on the corner of 71st Street and Union Avenue and called CPD, after not being able to find her guardian or parent.
She was fully clothed and wearing a jacket and hat.
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The girl did not have any apparent injuries, and was taken to Comer Children's Hospital in good condition, Chicago police said.
It's not immediately clear how she wandered into the street.
CPD said just before 7:50 a.m. she was reunited with her guardian, after police went door-to-door trying to find her family.
"Well, first of all, it's too cold out here, so now, you know, as a family man, I want to know where's your family? You know? This is heartbreaking," neighbor Vrsonic Smallwood said. "Crazy, but we pray for the best, and she's reunited, so that's the best thing."
Area One detectives are investigating, but police said the incident is currently classified as "non-criminal."
The Illinois Department of Children and Family Services was notified.