[6] However, exceptions to this rule were granted, as ten counties have areas below this size.

[7] Polk County contains the state's capital and largest city, Des Moines.

The Federal Information Processing Standard (FIPS) code, used by the United States government to uniquely identify counties, is provided with each entry.

This number is used for many governmental and organizational purposes, including state income tax preparation.

Finally, the number in the column headed "Map #" is used by the National Atlas of the United States, shown on the left; for purposes of the National Atlas, counties are numbered in geographical order beginning in the NW corner of the map.