A 13-year-old girl from the US state of Wisconsin, missing since her parents were discovered fatally shot in October, will be reunited with other family members on Friday, the day after she was found malnourished and dirty after apparently fleeing her captor.

Police said they had a man in custody in connection with the disappearance of Jayme Closs and the murder of her parents, James, 56, and Denise, 46, whose bodies were found in their home on October 15.

Jake Patterson, a 21-year-old Wisconsin man, was charged with two counts of first-degree murder and one count of kidnapping, Barron County Sheriff Chris Fitzgerald told reporters at a news conference on Friday.

"I just cried ... lots of happy tears," Jen Smith, the girl's aunt, told ABC's Good Morning America programme, describing when the Barron County Sheriff informed her that Jayme had been found alive.

The girl's disappearance in October made national news and stunned her hometown of Barron, Wisconsin, population 3,400, about 144km east of Minneapolis and sparked massive searches with 1,500 volunteers scouring woods and fields in suburban Minneapolis.

A $25,000 reward was offered for her safe return.

A woman walking a dog found the girl and knocked on the door of a neighbour's home and asked them to call the authorities, reported the Star Tribune daily newspaper.

"This is Jayme Closs!" the unnamed woman told Peter and Kristin Kasinskas, who live around 14km east of Gordon, Wisconsin. "Call 911!"

Gordon is located around 100km north of Barron, Closs's hometown.

The paper described her as thin and dirty with matted hair and wearing shoes that did not fit.

"'She's talking, she's doing very well,' they said," Smith told Good Morning America. Smith said she would see Closs on Friday afternoon.

Late Thursday, Barron County Sheriff Chris Fitzgerald said Jayme had been found in Gordon, but he had few other details.

"We promised to bring Jayme home and tonight we get to fulfil that promise," Fitzgerald said in a statement, thanking the community.