i read the illinois one a few months ago but i still prefer to have two side mirrors also
Mirrors. Every motor vehicle, operated singly or when towing another vehicle, shall be equipped with a mirror so located as to reflect to the driver a view of the highway for a distance of at least 200 feet to the rear of such motor vehicle.
I was interested in mirror and tire laws, and found this great website for all states. Massachusetts Lift Laws | Vehicle Modification Rules. MA 540CMR400 shows that only a rearview mirror is required in MA, unless there is obstruction of view through the back window, or excessive tinting.