She was walking near Walnut Street and 98th Avenue at 8 a.m. when the man forced her into an apartment and sexually assaulted her, a police spokeswoman said.
"According to her, she was threatened," said police spokeswoman Cynthia Perkins. "Being 13-years-old, she went with the man because he threatened her life."
The girl managed to escape when the man became distracted. She went to her school, Elmhurst Middle School, where officials reported the assault to police around noon. Police arrested the suspect at the apartment where the attack occurred and neighbors said he lives there. Authorities placed a child found in the home in protective custody.
The victim is being treated at a local hospital. The suspect, whose name has not been released, is undergoing questioning by police.