I've pulled 5er in IL for over twenty years First thing you do is call ISP and get a solid answer. As it will change from city to city and county. They are changing the laws in IL all the time. Like we used to have to get our trucks inspected once a year than they did away with it, now I buy a new truck 2014 and you best know the weigh restrictions with the new truck I can't use B-truck plates must have D plates and get truck tested twice a year or maybe pay a big fine. As far as I know the total length truck and any trailers 60 ft. I've talked to people who got ticketed for more than one trailer in IL.
"SO KNOW BEFOR YOU TOW"