Yep, it's either septoria leaf spot or it's alternaria leaf spot aka early blight. They are almost the same thing and at this juncture all you can do is to remove all of the affected limbs and burn them. After removing the limbs some folks spray the cuts with hydrogen peroxide but in your case its a little late for that. These fungal diseases are most prevalent during wet, warm humid weather and is caused either by soil splashing up on the leaves or the spores are blown in by the wind. Next year mulch under your plants and have a spray regimen of Neem Oil,horticultural cornmeal tea and a dusting of the base of the plants and the leaves with the cornmeal. You will probably still have a crop.
It certainly won't hurt anything and it might even slow it down some. After all, all you care about are tomatoes and not the plant.
