Green kyllinga is not a grass, it is a sedge. Traditional grass killers do not work on sedges, so you have to have a sedge killer. Hopefully the Dismiss label will tell you what it is. If your lawn is overrun with it, it is more likely to be nutgrass or nutsedge. Kyllinga is a slow moving plant while nutgrass is a very fast moving plant. The only way to tell them apart is to look at the seed heads (on Google Image Search).

Assuming it is nutgrass, did you get a lot of rain this summer or did you water the lawn more than one time per week? Because nutgrass is a swamp type grass that can be slowed way down by watering every week or two (or 3 or 4). Kyllinga is not a swamp grass and is not intimated at all by dry soil, but again, it does not spread nearly as fast as nutgrass.

So if this is nutgrass I would be inclined to wipe it out this season. If it is slower moving kyllinga, then wait until spring.

There's no need to aerate if you're overseeding (or for any other reason in my opinion). Why do you do that? I know a lot of people do it and you can find recommendations to aerate all over the Internet, but I don't think it's necessary (ever).

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.

Based on research, it looks like kyllinga. Has smallish, individual whitish balls. I don't think it's globe sedge as it appears globe sedge has bigger clusters as what I have is just random individual little seed heads. I do have nutsedge though too, just not as much of a problem as the kyllinga.

I would say it hasn't spread that fast, probably most of the summer. Honestly, I might have had it last year too but wasn't nearly as bad so I kind of ignored it.

Dismiss, based on research is said to take it out, and I've sprayed a mix on a few test spots. After 48 hours, the kyllinga appears to be starting to brown in those small test spots. I just wonder since I've let it go on for so long and it's now in some larger sections, should I just try to take it out now.

FWIW, it hasn't been an exceptional rainy summer here in NJ. I have the sprinkler system set to go off every 3 days but I often just manually start it based on the rain fall. Next year, I am actually swapping out some heads and planning on running the system one time a week for a long period to see how that works. But overall my lawn stays mostly green much of the summer save for real long dry spots like we are having now.

I aerate because there are parts of the lawn that just get compacted every year. I don't do it every year, maybe once every couple of years. This year it's due.

Thanks for your advice.

I disagree with letting either kyllinga or nut hang around, they both multiply pretty quick in my area. You got the right product though, dismiss is sulfentrazone based & will reduce their offspring