This is a tough time of the season for grass.  Rain is infrequent.  Temperatures are high.  Grass typically goes into a semi-dormant stage and browning can occur.  The grass has not died as the roots are still alive.  Do not be unduly concerned about the current state of your grass.  My guess that in another three weeks or so, your grass will appear green and vigorous.

But having said all this, there is a fungal disease that affects grass at this time of the year.  It is called brown patch and causes small brown spots to appear in grass similar to what you showed in your pictures.  It is especially common in Minnesota during times of high temperatures and high humidity.  These are conditions that we have been recently experiencing.  There is not much to do about this and is generally not fatal to the grass.  Here is some information about it: 

https://www.gardeningknowhow.com/lawn-care/lgen/brown-lawn-fixes.htm

If you have not done so within the past four years or so, I would strongly recommend that this fall (mid-September), you have your grass aerated.  Besides being a good turf practice, it will improve drainage in your yard for 2019 and may prevent your current situation from reoccurring..

Good Luck!!