We cannot say for sure what caused the decline of the turf.  Some causes of browning turf could be brown patch disease https://extension.umd.edu/resource/brown-patch-lawns, drought stress, grub damage https://extension.umd.edu/resource/identification-grubs-lawns, or possible fall armyworm damage. If the area browned out very suddenly (1-2 days) fall armyworms are a possibility, but it is too late to treat for them now. You did not mention the type of grass that you have and how you care for your lawn. If your grass seed contained some rye grass or other grasses, they can tend to die out in warm weather. 

Regardless of the cause of browning now is a good time of year to renovate and overseed cool-season turfgrass. Start by getting your soil tested by a lab. (Here are instructions on how to do so: https://extension.umd.edu/resource/soil-testing-and-soil-testing-labs). Having optimal soil pH and nutrients is essential for growing healthy turf.

Next, read through our instructions about the process of renovating turf (aeration, overseeding, and fertilizing) and care and maintenance after seeding.  https://extension.umd.edu/resource/lawn-renovation-and-overseeding

https://extension.umd.edu/resource/care-and-maintenance-lawn-after-seeding

Our Lawn Maintenance Calendar provides a step-by-step guide to the recommended lawn care practices to do throughout the season for a healthy lawn. https://extension.umd.edu/resource/lawn-maintenance-calendar-maryland-tall-fescue-home-lawns

You will have to monitor your new turf closely, check for a possible final generation of armyworms and determine whether control measures are necessary.

A “drench test” is a method to monitor for fall armyworms. Mix 3-4 Tablespoons of dishwashing liquid in 2 gallons of water. Pour this evenly over 1 square yard of turf. Watch the area for 10 minutes and count the caterpillars as they rise to the surface. Fall armyworm populations above 9 per square yard may warrant treatment.

Fall armyworms are more effectively controlled when the caterpillars are young and small -- greenish in color, less than 3/4". If you are seeing many fall armyworms (above 9 per square yard) in that stage, a lawn insecticide containing Bacillus thuringiensis, Spinosad or Acelypryn will kill the small caterpillars. Acelepryn (Chlorantraniliprole) is found in products such as GrubEx, but active ingredients can change periodically so check the product label to verify. Read and follow all instructions for the product you choose.

You can send us more photos if you notice additional symptoms.

Also, this is a lot of turf to take care of. You may want to consider some lawn alternatives to reduce the lawn area including pollinator gardens, beds and borders, etc. https://extension.umd.edu/resource/lawn-alternatives

Marian