Lawn was very lush up until late june this year. I have odd spreading brown patches. I can't tell what it's from. I checked for grubs and chit bugs and it was negative. We have a decent amount of rain recently and and it isn't coming back. Can I fix this with an overseed in sept?

Anything I do will likely be expensive since I have a large property. There is about 2000 sq ft of my yard that gets extensive shade and water drains into that looks great.

I've attached a pic and have many more that I can post if need be.

You didn't say whether you fertilize regularly. Turf grass is, like any other plant, needs food. A regular schedule of fertilizing keeps a lawn in good health and even if grubs invade, a turf that is in the best of health can fight it off.

I suggest you do an over layering of compost/triple mix or good topsoil...about 1/2" to 1" and do this every spring ....and fall.
Then an overseeding at the same times. What this does is builds organic matter into the soil, improves the soil to absorb and hold moisture and results in a tough turf that can stand up to the dry periods or the over-wet times.

To find out how much soil/compost to buy, simply measure the area you wish to cover...length times width...IN FEET.
Multiply that by the depth IN INCHES the soil you wish to put down...and multiply that figure by 3.....and divide by 1000.
The result will tell you exactly, in cubic yards, how much soil to buy.
Thus, if you were to cover the entire 1000 square feet with 1" of soil....1000 sq ft X 1" = 1000, then multiply that by 3...= 3000 divided by 1000 = 3 cubic yards of soil would cover the area.

By overlayering 1" of soil over the lawn every spring and fall will improve the drainage and water containment quality and improve the lawn's ability to grow grass in difficult times.
A good combination of seeds for northern areas is"
40% Kentucky Blue, 30% perennial ryegrass and 30% fescue.
This combo makes for a tough lawn that stands up to most what nature throws at it.

Some southern type grasses are quite different than northern ones...be sure to purchase from a qualified dealer who knows what type grass seed you wish and can advise how to keep it in good health.
Some southern grasses --such as Bermuda---cannot be oversprayed weed killer...it kills the turf as well.
From the picture I think you have a Kentucky Blue...I'm no expert at identifying grass types so be guided by what the experts advise.

The spreading brown patches are likely due to fungal disease, drought, heat stress, or a combination of any one of these factors. The brown patches may come back with cooler weather and rains, but disease can and does permanently kill grass, but not always. If the crowns are undamaged then the grass should return. A soil test would be a good place to start in determining what you need to add to your soil to make it a more conducive to supporting healthy grass.

goren - please stop making these recommendations. There really are many reasons it is bad advice. Unecessary cost & labor,the effect of adding 1" twice a year for several years, overseeding twice a year (especially in spring), etc. NOT GOOD!!!

How often do you water and for how long?
How high/low do you mow?
When were the last two times you fertilized and what did you use?

The disease diagnosis is the best. It will help to confirm when you answer the questions.

While such a volume of soil might be expensive to the average homeowner, the suggestion is to then do it according to your ability to cover such cost.
Expensive or not....the practice will improve a lawn.

I bow to experience of knowing individuals...but I assure you what I wrote is an accepted practice by those that know its benefits. LOOK IT UP in GARDEN JOURNALS.

The average homeowners' lawns are, without doubt, short on organic make-up. Without a soil test it is reliable way to help a lawn.

As noted, there any a thousand and one things that can affect the health of a lawn...but, unless the homeowner gets professional help he/she should try the simple approach...and not go overboard on well meaning, but amateur writers in garden chat rooms such as this.
Suggesting gloom and doom is not helping the writer. She should be encouraged to do the simple thing and see if that doesn't do the trick.
Laying compost on top of a lawn is never ...NEVER...bad for the soil.

I may not like tiemco's "bedside maner" and may disagree with him on some points like "disturbing the soil" and I may disagree at times with dchall's preference for organic solutions in instances where I think synthetics are more effective, BUT neither has ever given erroneous information on turf care.

Tiemco is one of the few knowledgable "amateur" generalists (expertise on seed, sythetics and soil) left here and dchall is extremely knowlegeable on organic care.

I believe they have been extremly diplomatic in correcting your mixture of accurate information and contradictory giberish to prevent people form wasting time, effort and expense by applying some of your advice.

If I'm wrong. please feel free to cite your "garden journal" references supporting your recommendations.