It is recommended that you keep your grass no shorter than approximately 3.5” and mow it as high as possible in heat and dry periods.  If you cut your lawn shorter, you will cause stress to the grass blades and root system, as well as promote disease and weed infestation.  Remember, too, to keep those mowing blades sharp.  You should be safely inspecting them a few times throughout the growing season.  Here’s a great publication from Purdue Extension on this topic:  Turf Maintenance