Delaware County is located in northeastern Iowa, in the second tier of counties west of the Mississippi River and in the third tier south of the Minnesota state line. It is partly in the Iowan drift soil area and partly in the Mississippi loess area and hence the soils are partly of glacial and partly of loessial origin.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 56—Delaware County Soils" (1929). Soil Survey Reports. 64.