As of September 2015, MapofUs.org publishes a map of Iowa that shows county lines. In addition, MapofUs.org has an interactive map that shows the history of the formation of Iowa's 99 counties.
In 1816, Howard County became the first county formed within Iowa, when it was a part of Missouri Territory. In 1834, after Iowa became part of Michigan Territory, Des Moines and Dubuque counties formed. Most of Iowa's southern and eastern counties formed during the 1830s and 1840s, after Iowa Territory separated. Most of the northern and western counties formed in 1851, and by the end of the 1850s, they were organized. Lyon and Osceola were the last counties to be organized, in 1872.