Rainey was found guilty this year of breaking into the now 89-year-old woman's apartment on January 1, 2015 and then sexually assaulting her at gunpoint in Westmont, some 40 kilometres west of Chicago, before forcing her to drive to an ATM to withdraw money.
Judge Telander sentenced Rainey to 60 years on a count of aggravated criminal sexual assault, and then gave him a consecutive 40-year sentence for armed robbery with a firearm, 'Chicago Tribune' reported.
A follow-up hearing in the case will be held on Thursday.
Rainey's defence attorneys expect to file a motion to reconsider his sentence. He already has been turned over to the Illinois Department of Corrections and is not expected at next week's proceeding.
He must serve 85 per cent of the 100-year sentence before he is eligible for parole. The woman declined to testify at the sentencing hearing, but her clear and credible trial testimony was a critical component of the prosecution case, said Assistant State's Attorney Mike Pawl.
"To be able to testify about something so unimaginably horrible with such grace and dignity was a tribute and a testament to her," Mr Pawl said.
The woman said at trial that she could not positively identify Rainey as her attacker, but other key details of her testimony were corroborated by evidence gathered by investigators, Mr Pawl said.
Rainey argued at trial that an acquaintance was the actual attacker, but authorities said they found both Rainey's and victim's DNA on the gun used that night, the report said.