Humboldt County is located entirely within the Des Moines Lobe of the Western Corn Belt Plains ecoregion, as defined by the United States Environmental Protection Agency (EPA). One of the flattest regions in Iowa, the Des Moines Lobe ecoregion is a distinctive area naturally defined by Wisconsin glaciation but modified by humans for extensive agriculture. In general, the land is level to gently rolling with some areas of relief defined by glacial features like moraines, hummocky knobs, and kettles, and outwash deposits. The lobe does not have any loess deposits like the Loess Hills to the west.