You need a soil test. And an expert opinion on the texture of the soil--at several different depths. Acid soil is possible (not likely in Illinois). Sandy soil is droughty and infertile of course. Yellow or red subsoil is poor quality and low in fertility.
And you need to decide for yourself--if the grass had enough water. Sunny spot? Was it hot in Illinois last year? LOL!
And secondly, perhaps the seed is a mixture of blue and rye--and perhaps only the rye came up, and you have no bluegrass. And some kinds of inexpensive rye are light green.
It might be easier to install sod--the high-quality types are very dark green types of pure Kentucky bluegrass. And the results are instant. Accept the check and go--same day. Not much soil preparation is needed. Do it tomorrow. Weather is good.