An interior rearview mirror system for a vehicle includes an interior rearview mirror assembly, a mirror casing, a reflective element, an information display, a compass sensor and control circuitry. The compass sensor is disposed in the mirror casing and has at least a first magnetoresponsive sensing element and a second magnetoresponsive sensing element. The information display is disposed behind the reflective element whereby information displayed by the information display is viewable through the transflective reflector by a driver of a vehicle when the information display is displaying information. The control circuitry determines a directional heading of the vehicle responsive to the sensing by the first and second magnetoresponsive sensing elements, and the control circuitry automatically compensates for a deviating magnetic field of the vehicle and generates a signal indicative of the directional heading of the vehicle. The information display displays the directional heading of the vehicle.