The crash happened around 1:55 p.m. at the restaurant at 2810 Route 34 in Oswego.
A 2-year-old boy inside the restaurant was killed, police said.
Eight people, including the driver of the vehicle, were taken to area hospitals for treatment, police said. Six people were treated at the scene and were released.
The driver of the vehicle was described as a 50-year-old woman who was the only occupant of the vehicle, police said. She was alert and was able to speak to officers at the scene, according to authorities. The cause of the crash was not yet known, but preliminary information showed it appeared to be an accident, police said.
The public was asked to avoid the area as police continued to investigate.
Police say some witnesses near the crash site rushed to help.
"As you can imagine, it was a chaotic scene when police officers and fire department personnel, firefighters and EMS arrived. They arrived on scene very quickly, and quickly began performing CPR and dealing with the injuries," said Oswego Police Chief Jason Bastin.
A witness who was at a nearby Chili's restaurant, Damaris Abella, told our sister station ABC7 in Chicago that she saw people running out of the Portillo's restaurant after a car drove through the front doors. She saw multiple people injured and being treated by emergency personnel.
14 injured after car crashes into Portillo's in Oswego, police say
Portillo's released the following statement:
"We are deeply saddened by the tragic accident involving a car that struck our Oswego restaurant this afternoon, and our thoughts are with those affected by this incident. As we continue to assess this unfolding situation, our primary concern is the safety and well-being of our guests and team members. We are grateful to the emergency responders who arrived quickly onsite, and we are working closely with local authorities to aid their investigation. At this time, the Oswego Portillo's restaurant will remain closed through the end of the day. We will defer all additional questions to local law enforcement."