The woman will be allowed supervised visitation with the boy and will retain custody of her other children.
Meanwhile, the boy's mother has been cited with class B misdemeanor reckless endangerment, according to West Valley City police.
Salt Lake City police, who had taken a missing person report from the woman, said they are still investigating the case.
The 9-year-old boy was riding a bicycle down I-215 in West Valley City at about 11:30 p.m. Friday, when a couple in a car spotted him, picked him up and took him to a nearby convenience story at 3500 South and Redwood Road, where they flagged down a police officer.
West Valley City police Sgt. Trudy Cropper has said that the boy did not know his last name or where he lived. The boy may have a speech impediment, Cropper explained, but seemingly did not suffer from mental impairment. He was also "very unkempt when we located him," Cropper added.
With virtually no information to go on, police took the boy to a care center for children while they searched for his family.
Investigators finally found the boy's mother about 8 p.m. Saturday.
According to Cropper, the Salt Lake City woman had visited a Salt Lake City business while searching for the boy Friday night. The business owner later saw a news report about the boy and put police in touch with the mother.
Salt Lake City police said the boy's mother had filed a missing-person report with them at 11 a.m. Saturday.