The woman told police the man poured gasoline on her body before lighting her on fire about 1:40 a.m. in the 10600-block of South Hoxie Avenue.
She ran to the firehouse at 105th Street and Hoxie in South Deering before being transported to Trinity Hospital, police said.
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She was expected to be transferred to University of Chicago Medical Center and was initially listed in critical condition, according to CPD.
No one was in custody later Friday.
Area Two detectives are investigating.