I was wondering when the best time would be for me to til my yard and plant new seed?

Question

I live in Central Illinois. We have dry summers, moist falls.

Answer 1

I would spray for weeds in late August. Till about 2 weeks later. Use a high quality grass seed mixture with fertilizer. Keep moist and watch it grow

Answer 2

In the fall.  Grass seems to grow better as newly planted, that time of year.