Investigators say 14-year-old Ashton Merritt died in the accident.
Merritt lost control and was ejected from the ATV. The vehicle then hit her as it flipped over.
Police say she was not wearing a seat belt or helmet, and the accident did not involve alcohol.
The passenger, 15-year-old Erica Whitfield, has suffered minor injuries and remains at Bay Medical Center.
The accident happened at about 11 a.m. Sunday morning at 500 Ike Steele Road.