Thank you for your question.  Your photos appear to show dollar spot disease, a collection of silver dollar sized tannish to whitish spots that can coalesce into bigger patches.  It starts with warm days and cool nights, prolonged leaf wetness, dew and high humidity and dry soil with low nitrogen fertility.
Cultural controls include:  
    a) maintain moderate fertility
    b) reduce compaction & limit thatch to <.75"
    c) minimize leaf wetness, water early in the day, when needed, to avoid drought stress
    d) plant tolerant cultivars 
Learn more about dollar spot and its control in the attached links:
Turfgrass Disease Chart-OSU (read the statement under the title)
MSU Turf disease ID
Purdue turf disease ID
Turf Diseases & Pests-PSU
I also recommend doing a soil test if you haven't done one in the past 2-3 years. Knowing the type and fertility (pH, macro-nutrient levels, CEC, etc.) of your soil is the starting point to establishing & maintaining a strong/thick turf that can resist diseases, weeds, moss and insects/grubs and look great without wasting material or $. More info here: Don't Guess-Soil Test-MSU and MSU Home Soil Test-self mailer    Soil test results will identify any fertility concerns that you can work to correct, to improve turf health (it’s a well spent $26). Your report will provide recommendations to correct deficiencies found, fertilizer type and a fertilization schedule.
More info on lawn care:
Benefits of Slow Release Lawn Fertilizers-MSU 
Fertilizing Home Lawns (E0001 TURF)-MSU
How to Choose & Apply Grub Control Products-MSU 
Lawn Irrigation Tips-MSU
Mowing Lawn Turf (E0013TURF) - MSU
Lawn Care - Illinois