By Agence France-Presse
The 87-year-old man was "located by a search and rescue team in his residence," said Bill Brown, the sheriff of Santa Barbara county.
Rescuers are continuing their search operations, with the missing now believed to number six, including a two-year-old girl.
Heavy rain on Tuesday, which followed 10 months of drought, sent sticky mud and debris flowing from the hills into Montecito.
In addition to the dead and injured, 65 houses have been destroyed while another 462 sustained damage.
Terrifying wildfires forced people to evacuate in December, and the mudslides struck just two weeks after they returned.
The fires burned most vegetation, leaving perfect conditions for the latest disaster to unfold.