I have to tell you that something similar happened to us last year, on a much smaller scale - we took a garden back to lawn, seeded it, and got an incredible number of weeds, some I had never seen before. I was prepared to have to reseed this year, and was pleasantly surprised this spring when most of them didn't come back. So there is hope.

For what it's worth: the light green fast grower (#5) is nutsedge, a nightmare to everyone who has it. Google it and get some ideas for how to get it under control.

#6 looks like purslane, but the picture is fuzzy so I'm not completely sure.

#7 is knotweed, another perennial pita.

I recognize most of the others but don't know the names. I think that keeping it mowed will help, and you'll probably have to spend a day or two pulling the worst ones up.

Good luck!

More weeds than lawn.

Suggest you start over. Then use the "stale seedbed" technique.

1 Kill all with weedkiller
2 Prepare the soil for a new seedbed
3 Water well and wait for 1st growth; let get several inches tall, then apply weedkiller.
4. After all is very dead, repeat #3.
5. Repeat #3 again. By now you should be having less re-growth.
6. If not, repeat #3.

When at a reasonable state, seed your lawn, then keep on top of each and every weed you see popup.

Oh boy. Thanks for the suggestions. I'm about to mow the newly seeded lawn to get a really good look at what fescue seed has actually grown from the seeding. I was going to avoid using chemicals, but I guess that would be difficult to do. The fall is coming up, so I guess now is the time to decide on a plan of attack and seeding.

I am always deeply grateful that almost all weeds are green - as long as you keep your lawn mowed,you can't tell if it's grass or crabgrass unless you really look.