A man whose 16 grandchildren were discovered living in squalid conditions at a home in rural southern Ohio, in the US, has been found mentally incompetent to stand trial.

On Wednesday, local time, a judge in Vinton County accepted the findings of an evaluation report for Gary Siders Sr.

Vinton County prosecutor William Archer did not object to the findings.

The 73-year-old grandfather appeared in court in a wheelchair.

His attorney, Dorian Baum, said after the hearing that Siders’s mєntal health had been declining for years and was “not restorable”.

“It’s not really a surprise to any of us that he’s not been found competent at this point,” Mr Baum said.

“He doesn’t fully understand or appreciate what’s going on.”

Siders was charged with 16 counts of child endangerment after his grandchildren were rescued on June 30 from a home in Hamden, about 129 kilometres south of Columbus.

The children’s parents, Elizabeth and Gary Siders Jr, and their grandmother, Christina Siders, were also charged. They have all pleaded not guilty.

Investigators said the children remained mostly confined to a 3.5-square-metre room in the house under appalling conditions for much of the past four years.

They were found with human waste all around.

“Most of our livestock was kept in better conditions than the children,” Vinton County Sheriff Ryan Cain said at the time of the discovery.

“Just a disgusting scene.”

The children were not enrolled in school and the family moved around southern Ohio over the past two decades. The family avoided leaving a paper trail, including birth certificates.

At the time they were found, the children ranged in age from 18 months to 18 years, with some described as “feral” and unable to speak. Authorities said their medical conditions varied.

“It was terrible,” Ohio Attorney-General Andy Wilson previously said.

“The 18-year-old can’t spell their name.”

The eldest was born in May 2008, two months after Gary Siders Jr, then 18, and Elizabeth, then 15, married at the Mason County Courthouse with her parents’ consent, according to court records.

Elizabeth has been pregnant most years since then, the records show.

Neighbours in the small town of fewer than 1,000 people said that they did not know children were even living at the house.

“My grandkids and my kids, we’ve all walked up and down that street. There’s never been a sign of any child,” one Hamden resident previously told WOWK 13 News.

“As a mother and a grandmother, I just don’t understand the logic.”

Since being removed from the house, the children have been placed in temporary state custody.