Hi, 

This looks like it is actually a native grass called Nimblewill, but it is often considered a lawn weed. It is a perennial so will grow in the summer and look green but tends to turn yellow and then brown through the fall and winter so many people that want a lush green lawn space don't care for it. 

When you visit the link you will find other pages explaining how to manage it effectively. Depending on your lawn conditions, you can aerate and overseed with a tall fescue blend that is formulated for the Mid-Atlantic, in the fall and this will help by outcompeting the spreading nimble will. If you wanted to do a lawn rehabilitation and their is a large colony of the Nimblewill, you may need to resort to chemical control  before overseeding with the desirable turf grass seed. 

Seeing that you are in Montgomery County you will need to refer to the pesticide laws for your county to make sure you are applying the products that are deemed 'safe' for use by homeowners. With any chemical, either non-organic or organic, make sure to read the product label and apply per the recommendations.  

Let us know if you have more questions on how to manage this. 

Emily 

you're welcome!