A tailgate illumination system includes an illumination device having (i) a tailgate bracket configured for mounting at a tailgate of a vehicle and (ii) a pivot bracket pivotally mounted at the tailgate bracket. The pivot bracket supports a light source that, when powered, emits light. With the tailgate bracket mounted at the vehicle tailgate, the pivot bracket pivots relative to the tailgate bracket responsive to gravitational force acting on the pivot bracket as the tailgate moves from a closed position to an opened position. With the tailgate bracket mounted at the vehicle tailgate, and with the tailgate in the closed position, light emitted by the light source, when powered, illuminates a ground region rearward of the vehicle. With the tailgate bracket mounted at the vehicle tailgate, and when the tailgate is in the opened position, light emitted by the light source, when powered, illuminates the ground region rearward of the vehicle.