Susan Schneider, the third wife of the star, is said to be arranging a service in the city's Bay Area, and this week family and friends started flying in ahead of the ceremony.
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Robin Williams' funeral service in reportedly taking place in the Bay Area of San Francisco
It will be an intimate send-off, with only Robin's loved-ones in attendance, including his three children, Zak, 31, Zelda, 25 and 22-year-old Cody.
"It's not official yet, but that's the plan," a source told E! News. "It will be small. They were both very private people."
The insider also said that a benefit night of comedy will be held for members of the public in honour of the late actor. It will reportedly take place in the next few weeks at the Throckmorton Theatre in Mill Valley, California, although nothing has yet been finalised.
Susan and Robin had been married since 2011. In a statement following his death on Monday, Susan said she was "utterly heartbroken" by the loss of her "best friend".
Robin Williams with his wife Susan Schneider and daughter Zelda
"This morning, I lost my husband and my best friend, while the world has lost one of its most beloved artists and beautiful human beings," she said.
"I am utterly heart broken. On behalf of Robin's family, we are asking for privacy during our time of profound grief. As he is remembered, it is our hope that the focus will not be on Robin’s death, but on the countless moments of joy and laughter he gave to millions."
Robin's children also all issued their own deeply touching statements.
The whole of Hollywood was shocked and saddened by the news that Robin had taken his own life, and many spoke out to pay their respects to the star.
Barack Obama, Prince Charles, Steven Spielberg and countless actors who worked with Robin were among those who shared their memories in a moving outpouring of tributes.