Kamiyah Mobley, now 18, was located in Walterboro, South Carolina, according to the Jacksonville Sheriff's Office, which confirmed her identity through DNA testing.
She appeared to be in good health and "a normal 18-year-old woman," Jacksonville Sheriff Mike Williams said at a news conference.
Authorities have arrested Gloria Williams, 51, in South Carolina on charges that include kidnapping. The victim believed the woman to be her mother, the sheriff said.
The case generated wide attention and led to more than 2,500 tips, the sheriff said, noting that authorities' investigation was still in the early stages.
The infant was kidnapped when a woman posing as a nurse grabbed the newborn from her mother's hospital room, according to the Florida Times-Union/Jacksonville.com.
Sheriff Williams said the woman's biological mother was "elated" when she learned the news earlier on Friday, but said it would be up to the victim to determine future contact.
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