According to http://www.hitchemup.com/statetowinglaws.htm two states - Wisconsin and South Dakota require brakes on ALL trailers. New York requires brakes in trailers over 1,000 lbs. Three backwards states, including my domicile, do not require brakes. Massachusetts requires brakes on trailers over 10,000 lbs and Alaska over 5,000 lbs. All others are somewhere in between.
The laws of physics state it is ALWAYS a good plan to have trailer brakes! The laws of physics trumps all state and federal laws!