Jefferson County is located in southeastern Iowa in the third tier of counties west of the Mississippi River and in the second tier north of the Missouri state line. It is entirely in the Southern Iowa loess soil area and practically all of the soils of the county are, therefore, of loessial origin.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 50—Jefferson County Soils" (1927). Soil Survey Reports. 47.