If you're asking about novels explicitly placed inside a county that’s legally named '
Delta County', the honest truth is that mainstream literature doesn't give us a huge, famous roster. There are a couple of real Delta Counties in the United States (notably in Colorado and Michigan), and those places show up more in local histories, regional fiction, and indie mysteries than in prize-winning national novels. What you do find in bigger literature is plenty of novels set in the Mississippi Delta — which people often shorthand as "the Delta" — and those capture the landscape, culture, and tensions you might be imagining when you say "Delta County."
For concrete, well-known examples: read 'Delta Wedding' by Eudora Welty if you want a Southern family saga drenched in Delta atmosphere; the book feels like the land itself is a character. 'Roll of Thunder, Hear My Cry' by Mildred D. Taylor gives you a child's-eye view of racism and resilience in rural Mississippi during the Depression. And although it's broader than just the delta, 'The Adventures of Huckleberry Finn' by Mark Twain traverses the Mississippi River from north to south and touches on that riverine world that defines the Delta in literature.
If your interest is specifically the named counties in Colorado or Michigan, expect to dig into smaller presses, local authors, or crime novels set in rural, Western, or Great Lakes backdrops — those books lean into small-town dynamics, resource conflicts, and wide-open landscapes. Personally I love the way Delta settings force writers to wrestle with history and weather and music; even when a county name isn’t spelled out, you can feel the delta in the tone.