Can you plant grass seeds in topsoil?

Yes, topsoil is a great soil to plant grass seed for your lawn.  The loamy texture allows roots to penetrate deep which promotes a healthy lawn.  Deep roots allows grass become drought tolerant during the summer.  A good topsoil also provides the nutrients needed to grow greener grass.  In Georgia, the red clay is nutrient deficient and compacts easily which makes it less ideal for grass than topsoil.