A psychologist found the victim, a 48-year-old woman from Morrinsville, had an extremely low IQ based on an Adult Intelligence Assessment Scale.
In the decision from 2007, he said "99.9 per cent of people her age would function better" than she.
The victim behaved like a 5-year-old and would often go on walks without telling anyone.
Justice Williams said she was rated as being severely "subnormal" and unable to consent to sexual acts.
The assault happened on July 22, 2006, when Wilson was wandering Morrinsville trying doors of houses with a view to burgling them.
He went to the victim's house to borrow money. As he left, he claimed she followed him to a school where the pair had sex. He was arrested soon after.
Wilson, who already had 63 convictions and had just been released from prison when he offended this time, is now serving his extended supervision at Hampton Downs under the supervision of Anglican Action.
The first of his latest breaches was on May 5, when he drank alcohol and smoked cannabis with other residents.
He returned a positive test for alcohol on June 21 and on July 23 he and another resident went to nearby Mercer and bought a dozen beers.
They consumed it at an abandoned petrol station near the accommodation before returning and being spotted "stumbling" by Corrections staff.
Wilson's counsel David Allan told Judge Stephen Clark his client had served 12 1/2 months in prison for other breaches over the past seven years.
He was initially living in Hamilton, and wanted to go back there, but was moved to the accommodation near Spring Hill prison, "for a variety of reasons".
Allan explained that when Wilson leaves the accommodation, which he is freely able to, and returns he begins to feel "hopelessness because he can't see a way out of there".
"He has been told by Corrections and Anglican Action that he needs to [be] drug-free for an extended period of time and then he can be transitioned but he has found it difficult to stay alcohol and drug-free.
"Ned would like to be able to get into Hamilton to live and spend more time with his parents."
Before his offending, Wilson got into "difficulty and spent a bit of time on the streets, drinking excessively and being transient".
He served his whole seven-year sentence before being released and a positive out of all the breaches was that none had been for sexual offending or entering Morrinsville again.
Allan accepted there was no other option but prison for his client but urged the judge to "exercise some leeway" in the jail term as he would have to start his rehabilitation all over again.
Wilson had suffered severe trauma as a child; an accident that deformed his skull, then visiting a neighbour only to find them murdered, along with witnessing domestic violence at home.
"But overall he considers his parents were very good to him and he takes responsibility for the mistakes he's made in life and getting into situations where he didn't exercise good judgment."
When questioned by the judge about options, a probation representative said they had "exhausted pretty much every avenue we can".
"At 50 years old, when it comes to being peer pressured by your friends, it just comes down to making better choices."
Judge Clark agreed jail was the only option, handing down a five-month term.
