Marin County Sheriff's Office confirmed that the actor was found unconscious and said it was carrying out a comprehensive investigation to determine the exact cause of death.
Mr Williams was famous for films such as Good Morning Vietnam, Mrs Doubtfire and the Dead Poet's Society.
He was nominated for a Best Actor Oscar on three occasions, and took home an Academy Award for Best Supporting Actor for his performance for Good Will Hunting in 1997.
Mr Williams's publicist said he had been suffering from severe depression recently.
In a statement, Mr Williams's wife Susan Schneider said: “This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings. I am utterly heartbroken.”
Marin County Sheriff's Office said: “An investigation into the cause, manner, and circumstances of the death is currently under way”.
A forensic examination is expected to take place today, with toxicology tests to take place later.
Police are not believed to be looking for anyone else in connection with the death.
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HELPLINE NUMBERS AFFECTED BY SUICIDE
And if you have been affected by this story or are experiening mential health difficulties there are a number of agencies that you can reach out to
HSE South Suicide Prevention Helpline 1800 742 745
Console – 1800 201 890
1 Life Suicide Helpline – 1800 609 090
Samaritans 1850 609 090
Farm and Rural Stress – 1800 742 645
Pieta House Roscrea – 0505 22568
Or you can text HELP to 51444
