I live in the Chicago area and a small dead spot started in July and has grown to this. Even though I dug up portions and didn't see any grubs, I treated for grubs. I contacted the county extension office over a month ago and have not received help there so if anyone can offer any thoughts on what I should do to prevent more lawn dying and how to repair this I would appreciate it. If repair suggestions involve renting equipment, could you suggest professionals who might do the work since I am a 60+ single woman and can only do so much. I also haven't had any luck finding "lawn repair" professionals in my area and lawn care services just mow, they don't fix lawns. Help? Thank you so much for any advice!
Keep in mind that many "lawn" species are soft grasses that appreciate a cool and moist environment. This is particularly so in the temperate regions of the world. So a soil type that can absorb and retain moisture without letting it go too quickly is most likely to support nice grasses. Since this suddenly started happening, and the soil type is not likely to change quickly unless someone poured a toxic substance on the ground to effect a sudden change, it's not the soil type at fault but perhaps something else. If a building no longer provides shade, or a tree was removed on your property or nearby then the summer sun might be having a more dramatic effect on that patch.
Consider two experiments that will give you more information: take a "mason jar soil test" using samples from the lush green grass area and compare to samples from the bare area, and watch how the sun traverses your lawn area to see how many hours of direct sun the various areas receive. You may find that the bare area gets much more sun and drains too rapidly to support nice grasses.
As long as there has been no dramatic event such as a toxic spill, eventually a group of weeds will find the bare area attractive because there will be little competition. Coarse grasses, clovers, weeds will find it and try to establish themselves. So that is one scenario where no action is required. Mow high, get a bag of clover seed and scatter, and keep an eye out for neighbours with light, dry soil where something is flourishing.