We all know that filming locations can change, and until filming is confirmed it is speculation. During a press interview to promote Broken City, Mark Wahlberg stated that he was looking for a house to rent in Chicago while filming Transformers 4 this summer.
Of course we know that Transformers 3 filmed a good portion of their scenes in Chicago and Bay frequently praised the city. It's not too far fetched to believe that filming for TF4 will occur, at least partially in the Chicago area.
We will see. If you are in the Chicago area, keep an ear and eye out for information about filming or extra casting calls. As we get more information, we will pass it along to you.