The fire was reported by a passing motorist shortly after 12:45 a.m. at the Los Robles Mobile Home Park, located in the 400 block of San Paulo Way, Novato Deputy Fire Chief Eric Nickel said.
Firefighters arrived to find a mobile home fully engulfed in flames and at least two adjacent homes were threatened.
Residents of the threatened homes were safely evacuated, but intense flames prevented firefighters from gaining access to the burning structure.
The blaze was controlled in about 15 minutes and did not spread to the neighboring homes, Nickel said.
When firefighters entered the burned home, they found the body of an elderly woman in the bedroom. The woman's identity and cause of death has not been released by the Marin County coroner's office.
Fire investigators will be working today to figure out what caused the blaze, which mostly burned in areas of the home away from the bedroom, Nickel said.