Rockford is not a suburb of Chicago. It is a small (post industrial decay) city in its own right. It has its own suburbs. Few commute from Rockford to Chicago, and the train gets no closer than Elgin.
It would guess West Side, but the photo appears to be closer to the downyown area.
Right you are. I grew up in Rockford, but live in Loves Park now. Not far from that part of town.