Clay, clay, and more clay...almost every home in the Springfield area has to combat tough clay conditions with their turf. It seems the contractors take all the good topsoil away or the over-dig of the house is all clay and spread out over the yard to get rid of it.
Sod seems to do fairly well on clay, as long as it has been tilled just a couple of inches down. You might ask why not take the tilling of the sod a bit deeper? Basically it is just going to settle and be unstable for a couple months. As you walk on it, mow it, or even water it, the soil moves all over the place, leaving behind ground that sits at a very poor grade.