15-year-old Natalie Lyons was located at a home on Copeland Mill Drive and deputies arrested the man she was living with, according to Lowndes County Sheriff Chris Prine.
An informant with Silent Ministries Children Services tracked down Natalie Lyons and alerted deputies.
When investigators arrived at the home, they discovered she'd been living with a man twice her age.
Neighbors knew her as Angie, the man's 18-year-old girlfriend.
Around 7 p.m. Sunday night, Lowndes County investigators say they found Lyons in the back yard with Michael Rounds, 29.
She was considered an "endangered runaway" by the National Center for Missing and Exploited Children.
When deputies searched Rounds' home, they say they found a bullet proof vest and two pistols--one in a holster next to Rounds' bed and the other hidden under his mattress.
Investigators say one of them had been stolen from Carlton Outdoors in Valdosta.
Neighbors say Rounds and Lyons moved from Statenville just three days ago.
"It's just an older guy taking advantage of children, you know," said Paul Brooks, who bought a home next door a month ago. "She's just a child. She should be in school."
"The parents should have been on this child a little closer about her whereabouts day and night," said Phillip Jackson, who lives two homes down and moved to the neighborhood nearly four months ago. "Cause if my daughter is missing--two minutes-- I wanna know where she at."
Rounds, who's behind bars at the Lowndes County jail, is charged with stealing that pistol and interfering with child custody.
Lyons was released to her parents at the Lowndes County Sheriff's Office and is now back in Jacksonville.
But officers are investigating why she ran away from home in May.