Possibly Chickweed, a plant that grows best in a soil that lawns really like, a rich, near neutral soil. Chickweed is a cool weather annual and so it will die off as temperatures rise. Your Ohio State University Cooperative Extension Service can be of help as could this from Penn Sate. http://extension.psu.edu/pests/weeds/weed-id/common-chickweed kimmq is kimmsr

Yes, I recognize this is an old post, but for the benefit of others landing on this page... I'm 99% sure this is Creeping Beggarweed or Spanish Clover (D. incanum/D. laxiflorum). Mine produce a deep pink, almost purple flower. I spent an exhaustive afternoon in my back yard digging a ~6' x 6' patch of it out of my St. Augustine about 2 yrs. ago. I would compare the underground root system to that of Torpedo grass... invasive and virtually impossible to eradicate. My temporary joy of digging out the mother lode tap root (at least 10" deep!) was quashed when sprigs of it started popping up again. As the natural/organic method failed, I got some Roundup. The grass has almost fully recovered now; I get an occasional sprig though. Then I noticed it was invading a stretch of front yard near the street. Mother Nature sent Irma to help me with that area. Put the debris pile on top of it and by the time it was picked up, mostly everything was dead underneath. It made it easy to pull most of the roots out then. So for the sprigs that have survived both there and in back, I take a can with both ends cut off, slip the weed inside of it (Beggarweed and/or Torpedo), and try to protect the surrounding St. Augustine as I spray the Roundup. My condolences to anyone battling this... good luck!

Looks like yellow nutsedge to me. If you pull one up and roll it in your fingers, do you feel 3 edges? Remember that sedges have 3 edges. They are neither a grass or a broadleaf weed. Nutsedge produces hundreds of thousands or millions of tiny tubers or "nutlets" as part of its rhizome network. The tubers are viable for years and can germinate at almost any time. They are controlled with herbicides like Halosulfuron methyl (Sedgehammer).

dchall_san_antonio, sorry I didn't include. I am in Zone 6B, on the South Shore of Massachusetts.