Benton County is located in eastern central Iowa in the fourth tier of counties west of the Mississippi River and in the middle tier of counties It is partly in the Mississippi loess soil area and partly in the Iowan drift. Hence the soils of the county are partly derived from loessial material and partly from material of glacial origin.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 46—Benton County" (1927). Soil Survey Reports. 51.