There is a small family owned business near O'hare that fills 5lb tanks for $6 (including tax). If you need a tank recertified, he'll do it free with tank fill up.
He was willing to fill up my old 5lb SSP tank & mentioned that others might not fill it, so just bring it back here. He said most places won't fill it unless it has the newer triangular shaped knob used on the newer overfill protection devices, but because he knows this one has overfill protection device so he filled it.
Since, I don't want to get him in trouble because I don't know if it is legal (so far, some quick research indicates it only need an overfill protection device, not necessarily the one with the newer triangular knob), PM so that it doesn't show up in a Google search. Just in case it is not legal, I'll give a recommendation for a small family owned business near O'hare, but I will NOT confirm whether it is the same place mentioned here.
Also, if you want a 20lb tank filled, he fills it with 20lb not like those exchange places that are usually only filled at $15.