Mills county is located in southwestern Iowa, in the second tier of counties north of the Missouri state line and separated from the state of Nebraska by the Missouri river.. It lies entirely within the Missouri loess soil area and the upland soils of the county are all of loessial origin. The bottomland soils are likewise loessial, being made up of material carried from the uplands by the streams, reworked and laid down on the terraces and bottoms.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 33—Mills County Soils" (1924). Soil Survey Reports. 45.