Usually there is crabgrass in a spring-seeded lawn, but you managed to keep it out.

Where do you live?

Can you get the Guaranteed analysis from the bag of grass seed. That will likely give us a clue as to what the coarse bladed grass is.

Dead grass in a spring seeded lawn is par for the course. It is possible the grass is not dead but only dormant. Again, need to know where you live and what was in the bag.

Thanks for the response, I live in Canada 70 miles north of Grand Forks ND. (Zone 3)
I will check with the company I purchased it from tomorrow and post the GA
then. Should I rake the lawn or just leave it just in case the brown stuff is just dormant?

Kentucky bluegrass is a fine bladed grass compared to the coarse blades in your picture. I think the problem is in the seed, but not the KBG.

Ok, I just checked the website and the guaranteed analysis of the seed I used is 40% KGB 40% creeping red fescue and 20% diploid annual rye.

Two turf grasses and a forage grass. That's weird. Did they mention the varieties of the grasses? Like they might have said, "Chewing's red fescue" or something like that. If they don't mention the varietal name, and if they quote percentages that happen to be rounded off to the nearest 20 and add perfectly to 100%, then I get suspicious. It should mention varietal names and the percentage should be out into 3 decimal places. They should list 0.023% weed and 0.402% Other Crop, for example. Or they might have 0.00% weed and other crop. It happens. But some weed seeds are very light weight and can fill your lawn with a mess before you know it.

Anyway I can't find a picture of the rye forage grass, but they all call it an aggressive growth type of grass. Being an annual grass, it will not persist through the winter. It may come back next spring from seed. Both of the other two grasses should form an amazingly dense turf that fights off weeds, though. Keep it mowed at 3-4 inches (I lean to 4). The additional shade from the tall grass helps fight off weed seed germination. Most importantly be sure you allow the soil to dry out at the surface before you water.

The dead grass among the healthy is likely to be KBG that has gone dormant. It will come back. KBG turns brown in winter and it can turn brown in summer when it gets too hot or is not watered deeply once a week. It might be possible the dead grass is the annual rye which is actually dying.

Eventually this should be a great looking lawn. I like both the KBG and the creeping red fescue.

Should I overseed with the same seed or should I just put down KGB and creeping red fescue and leave out the diploid annual? Also For overseeding should I use a broadcast spreader or do I need to rent an over seeder?

I would leave out the annual grass. It's just annual. You would need to redo it every year if you liked it.

Handheld broadcast spreader is fine.

Should I aerate before overseeding this new lawn. How much seed should I put down?

No need to aerate...ever...unless you feel a need to make some guy's boat payment for him. Aerating is a lot of work and does not accomplish what most people do it for. If you have hard soil and want to soften it, search this forum for my thoughts on using shampoo to soften the soil.

For the seed, read the bag/box for directions. Some seeds are coated and the poundage (kilogramage??) per square area is different for those.

My plan is to overseed in the middle of Oct. then maybe toss a 1/4" of topsoil mixed with peat moss on top to help keep the seed moist in the spring. Can I spray with shampoo now? Or will it effect the germination of the seed in the spring in any way?

From my soil analysis done in the spring my organic matter is high at 14% . if I cover the seed with 1/8" of compost after over seeding would that be a bad idea? I'm concerned about the high organic matter content in the soil.