A fog detecting system for a vehicle includes a camera disposed at a vehicle and having a field of view forward of the vehicle, and a non-imaging sensor disposed at the vehicle and having a field of sensing forward of the vehicle. The camera captures image data and the non-imaging sensor captures sensor data. A control includes at least one data processor operable to process image data captured by the camera and sensor data captured by the non-imaging sensor. The control, responsive to processing of image data captured by the camera and processing of sensor data captured by the non-imaging sensor, determines presence of fog ahead of the vehicle and in the field of view of the camera and in the field of sensing of the non-imaging sensor.