The victim, who lives on the first floor of the house that burned, located at 10905 Ogburn Lane, was taken to Santa Rosa Memorial Hospital, Forestville Fire Protection District Chief Dan Northern said.
His name was not immediately available.
The fire was reported at the two-story, wood-frame home in west Forestville at 1:07 a.m. The second floor was engulfed in flames when firefighters arrived at 1:16 a.m., Northern said.
The woman who owns the home, her teenage son and a man live on the top floor, Northern said. The owner was asleep and her son had just arrived home when the fire broke out, Northern said.
The blaze was controlled at 1:47 a.m., but crews remained at the scene until around 4:30 a.m., Northern said.
The fire caused an estimated $150,000 in damage.
It is believed that the blaze started near a couch on the home's front porch area, Northern said. There was no obvious electrical or other ignition source and the cause has not been determined.
The fire destroyed the second floor, but the owner declined an offer by the American Red Cross to set her up with temporary housing, Northern said.
Firefighters from Graton, Monte Rio, the Russian River Fire Protection District and Rincon Valley responded, and the Windsor Fire Protection District provided mutual aid.