The crime did not occur, Kendall County Detective Sgt. Joe Jasnosz said Thursday night.
The woman had claimed she was attacked after being pulled over Tuesday night by a man dressed as a police officer or security guard who used an emergency light on his vehicle just west of Plano.
The woman, 33, from Sandwich, told police she was attacked about 6:45 p.m. in a field off Griswold Springs Road, about 1/4-mile west of Little Rock Road, in an area just west of the border of Plano in Kendall County.
The report the woman provided included details like the man had been driving a blue Ford Crown Victoria with a blue-and-red emergency light on the front of the car, the Kendall County Sheriff's office had said.
The man was wearing a uniform like one worn by police, security guards or firefighters, and he pulled a mask down over his face and produced a gun, the woman claimed, before he led her into a nearby cornfield, hit her and sexually assaulted her.
The woman had provided a description of the alleged attacker as an Hispanic man, with a light or tanned complexion, standing about 5-foot-8 and weighing about 180 pounds.