Adair county is located in southeastern Iowa, in the third tier of counties north of Missouri and the third tier east from the Nebraska line. It. lies partly in the Southern Iowa loess soil area and partly in the Missouri loess. The soils of the county are largely loessial in origin, but in the Southern Iowa loess section a large part of the area is covered by a drift soil derived from the underlying drift formation, from which the thin covering of loess has been entirely removed.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 27—Adair County Soils" (1922). Soil Survey Reports. 25.