As part of the sentence, the judge also ordered him to pay a fine of $25,000 plus the costs of prosecution.
Montgomery County District Attorney Kevin Steele rejected the call for a softer punishment.
Chief accuser Andrea Constand stood next to Steele at a news conference but did not address the media.
Cosby did not make any statement before sentencing. Corrections officials at Phoenix will assess Cosby's needs to determine where he'll serve the bulk of his state prison sentence.
But only one case had not surpassed the statute of limitations: the alleged assault of Andrea Constand.
Cosby's lawyers have already said they plan to appeal his conviction, and he has denied any wrongdoing.
Judge Steven O'Neill sentenced Cosby on Tuesday to three to 10 years in state prison.
The sitcom was a fabulous success, turning Cosby into a major figure of U.S. pop culture in the second half of the 20th century. O'Neill says Cosby had no right to it.
Cosby made clear in that testimony that he had no verbal consent to engage in sexual contact with the woman, and without it, he was breaking the law, the judge said. O'Neill chose to merge the sentences because they stemmed from the same event, which meant the maximum was 10 years in prison, according to the Times and prior coverage by the Legal Intelligencer.
The sentence was reduced from a maximum of 30 years. Mr. Cosby, this has all circled back to you.
Ahead of the sentencing, Constand wrote a five-page letter to the court explaining how Cosby's assault - and the ensuing legal battle - had changed her life. About 60 women have accused the man once known as "America's Dad" of sexual misconduct.
In April, a court in Pennsylvania found him guilty of drugging and sexually assaulting a woman in 2004. Courthouse witnesses say Cosby emptied his pockets and removed his tie before being taken into custody. According to reports, the comedian molested and drugged the woman at his Philadelphia estate.
Oil producers to continue working to boost output
That suggests OPEC's power to influence the market will be tempered by USA production for about another decade. It said demand for its crude would rise by 7.3 million bpd to 2040 and for all its liquids by 10.5 million.
"The next morning I woke up, and I wasn't wearing my pajamas", she said.
"Do you understand that the judge has determined that you qualify as a sexually violent predator?" one of the prosecutors asked.
Under that designation, Cosby will have to undergo monthly counselling and register as a sex offender with police for the rest of his life. He could eventually be sent to a state prison that has separate units for geriatric prisoners and programs for sex offenders.
Disgraced US comedian Bill Cosby, 81, was sentenced to at least three years in prison on Tuesday.
Before handing down the prison sentence, Judge O'Neill also chose to designate Cosby a "sexually violent predator" under Pennsylvania law.
In a 2014 interview with ET Online, Dickinson said Cosby drugged and raped her in 1982 after dinner in Lake Tahoe.
She has been plagued by overwhelming fear, self-doubt, and isolation, she said.
Born on 12 July 1937 in Philadelphia to a maid and a Navy cook, William Henry Cosby Jr. quickly emerged as the class clown, and joined the Navy after 10th grade, finishing high school by correspondence.
The judge said that Cosby "could quite possibly be a danger to the community".
Ebonee Benson, another of Cosby's publicists, read a statement from Camille Cosby, Cosby's wife, who was notably missing from the sentencing hearing. Cosby did not testify at either of his two trials.
Prosecutors are asking for a sentence of five to 10 years in prison.
Cosby, whose estimated fortune once topped $400 million, broke barriers in the 1960s as the first black actor to star in a network show, "I Spy".