Hardin county is located in central Iowa in the fourth tier of counties south of the Minnesota state line and in the sixth tier west of the Mississippi River. It lies partly in the Wisconsin drift soil area and partly in the Iowan drift and Southern Iowa loess areas. The soils of the county are therefore of glacial and loessial origin, the major portion of the area being covered by glacial soils.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 38—Hardin County" (1925). Soil Survey Reports. 39.