The crash happened around 12:45 p.m. in Schell-Vista in the area of San Luis Road and Broadway south of Sonoma, according to a Sonoma County Fire and Emergency dispatcher.
The plane was a single-engine Cirrus SR22 with four people on board that crashed in a field about 1,000 feet west of the airport, Federal Aviation Administration officials said.
Three people went to hospitals, two by helicopter and one by ambulance, according to the fire dispatcher.
The Schell-Vista Fire Protection District and Sonoma County Sheriff's Office responded to the crash.
An investigation into the crash by the FAA is underway.