His widow Susan Schneider said in a statement tonight the Mrs Doubtfire star "was not yet ready to share publicly" his stuggles with the crippling condition.
She said he was sober at the time, effectively rebutting claims he was still battling alcohol problems at the time of the tragedy on Monday.
Parkinson's is an illness that is also suffered by Mr Williams friend, Billy Connolly.
The 63-year-old actor was found dead in an apparent suicide in his home near San Francisco.
"It is our hope in the wake of Robin's tragic passing, that others will find the strength to seek the care and support they need to treat whatever battles they are facing so they may feel less afraid," Susan Schneider said.
Connolly - who is eight years older than Williams - was diagnosed with Parkinson's disease and prostate cancer on the same day in September last year. He dealt with the news at his home in New York by blowing a raspberry.
Williams, who received an Academy Award for his role as a teacher in Good Will Hunting and won legions of fans for comedy roles in movies such as Mrs Doubtfire and Good Morning, Vietnam, was discovered by his concerned employee.
Marin County's assistant chief deputy coroner, Keith Boyd, said Williams died by asphyxia. His death is being treated as suicide, although investigations are still continuing. No date has yet been set for his funeral.
Williams had attended a Highland Games at Lonach with Connolly, where the US star took part in a fun run. The Glasgow comic owned the nearby Strathdon estate.
Connolly has paid tribute to Williams as "both my friend and my hero, a unique talent and a kind and generous man; the world will be a much poorer place without him."
Connolly's wife, Pamela Stephenson Connolly, added: "Robin was one of the most uniquely brilliant and complicated comic artists the world has ever known."