Links
Atlas of Historical County Boundaries
The Newberry Library provides an interactive map, county chronologies, and other resources to learn how county boundaries in the United States formed and changed.
Atlas of the Historical Geography of the United States
The Atlas was originally published in the 1930s. The maps have been georeferenced to be used in an interactive map and allows the historic maps to be viewed in a new environment. A few examples of the available maps are transportation, political, settlement, and military.
David Rumsey Map Collection
David Rumsey is a private collector of maps and is digitizing his collection of maps to be viewed free-of-charge by users.
Illinois County Boundaries, 1790 - Present
PDF of maps showing the county boundary changes and newly created counties in Illinois.