A boy allegedly abducted in a custody dispute nearly two years ago has turned up alive, hiding with his mother in a small, specially built secret room at his grandmother's home in the US state of Illinois, investigators say.

Richard "Ricky" Chekevdia, who turns seven on September 14, was in good spirits and physically fit after being found on Friday by investigators with a court order to search the two-storey rural home in southern Illinois' Franklin County, about 200km southeast of St Louis.

The boy's mother, 30-year-old Shannon Wilfong, is charged with felony child abduction. The grandmother, 51-year-old Diane Dobbs, is charged with aiding and abetting. The two women remained in jail on Saturday.

The boy was staying on Saturday with one of his father's relatives while state child-welfare workers investigate claims the father abused the child before his disappearance - allegations rejected by the dad, who's thrilled the agonising search has ended.

"Two years? You have no idea," Mike Chekevdia, a 48-year-old former police officer who's a lieutenant colonel in the Illinois National Guard, told The Associated Press by telephone on Saturday from his house about 5km from the home where his son turned up. "I've lost sleep. I've lost weight. I've gained weight. I wouldn't wish this on anybody."

After hearing his son had been found, Chekevdia said: "You could have knocked me over with a feather."

Chekevdia won temporary custody of his son shortly before the boy and his mother - Chekevdia's former girlfriend - disappeared in November 2007. Chekevdia said he long suspected his son was being hidden by Dobbs, although there were no signs of the boy at her home when it was searched with her consent after his disappearance. Wilfong was charged in December 2007 with abducting the boy but couldn't be found.

For much of the time since, Chekevdia said, the windows of Dobbs' home were blocked off by drawn shades or other items, presumably to prevent anyone from peeking inside.

"I had a firm belief he was in there, and yesterday (Friday) it was confirmed," Chekevdia said.

Investigators, during a news conference on Friday, did not detail what led sheriff's deputies and federal marshals with a search warrant to Dobbs' house on Friday, when they found the boy and his mother in a hideaway roughly 1.5 by 3.5 metres and about the height of a washing machine.

"We let him out of the (patrol) car and he ran around like he'd never seen outdoors. It was actually very sad," Illinois State Police Master Sgt Stan Diggs said. "He was very happy to be outside. He said he never goes outside."

"Surprisingly," Diggs added, "Ricky is in very good spirits. For someone who's been isolated in that house with no other outside beings, he's a very social, very polite, very talkative little boy."

Dobbs, the grandmother, told the Southern Illinoisan newspaper of Carbondale, Illinois, last year that her daughter had been forced into hiding to keep the child from his father. Dobbs called the custody dispute a "nightmare for all of us".

Chekevdia, eager to get his son back in school and to a dentist, said waiting for Ricky to resurface required patience.

"It's hard to sit back and watch things happen when you're used to making things happen," said Chekevdia, a military officer who served in Iraq earlier this decade. "But I just bided my time and let the system work."

AP