There are two groups or broods. One is the 13-year and the other is the 17-yr. Could be trillions of cicadas. Illinois and Iowa are the areas where both groups will appear. There's also a map highlighting the most affected areas. One is southeast United States and the other is Midwest. Apparently when the soil reaches 64° followed by a warm rain is when they will emerge, usually mid-May through June.
Steve M