Clay county is located in northwestern Iowa, in the second tier of counties south of the Minnesota state line and the third tier east of the Missouri river. It is bounded by Dickinson county on the north, O ’Brien county on the west, Buena Vista county on the south, and Palo Alto county on the east. It is entirely within the "Wisconsin drift soil area and most of the soils are of glacial drift origin.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 12—Clay County" (1919). Soil Survey Reports. 12.