Did you spray anything on them?

nope - no spray. And they are just random within a row.

molat, Have you had torrential rains? I suppose that could hurt them...especially with mulch to keep them wet.

Gophers maybe?? Try tugging upward on one, gently. Is it loose?

Kevin

I hadn't thought of gophers or too much moisture. I don't think it is gophers - haven't seen any other evidence but I will look closer.

I had watered the area two mornings in a row because the corn in the area had leaves that were starting to curl because of lack of water. We haven't had substantial rain since the massive amount we had in May. But I do have the peppers mulched with grass clippings while there is nothing on the corn. I'll check into whether it is too wet.
If I pull away the mulch and let the sun do it's work would these plants come back or are too far gone? I may remove the mulch from everything else just to prevent further loss.

Thanks again for the suggestions.

Just wanted to say sorry that happened. I just lost a zucchini plant that wilted over night as well.

Grass clippings - could there be herbicide residue on the clippings?

The tan spots between the veins in the leaves (see the final picture) shows the plant ran short of water, probably on an excessively hot day.

Indicates a root problem of some kind.
Dig it up -- not pull -- and take a picture of the roots, then please post it for us.

Strange. That can only happen if someone was chewing on the roots. Chemical residues or imbalance would effect plants around it, and probably wouldn't cause it to wilt badly overnight. Dehydration and insect damage would also show up in the plants next to it. Brown spots may not be related.

I suppose some kind of disease is a possibility, but if so, you'll very quickly see it on adjacent plants, and it wouldn't choose targets randomly in a row.

I did dig up one of the wilted plants and tried to preserve as much of the root system as I could.

The grass clippings wouldn't be the cause as my lawn has not been treated.

In the past two mornings, I have not had any more peppers wilt. So I'm leaning towards too much water as a cause.- even though we are very dry here. I had watered two mornings in a row and when I dug up the pepper it was not dry but dark, black, and crumbly. Seemed about ideal for growing here in Iowa. I've grown peppers for many years and have never seen this - even in rainy years. But that sounds like the best explanation.