Atlas of Historical County Boundaries
The Atlas presents in maps and text complete data about the creation and all subsequent changes (dated to the day) in the size, shape, and location of every county in the fifty United States and the District of Columbia. It also includes non-county areas, unsuccessful authorizations for new counties, changes in county names and organization, and the temporary attachments of non-county areas and unorganized counties to fully functioning counties.
The principal sources for these data are the most authoritative available: the session laws of the colonies, territories, and states that created and changed the counties. The Newberry Library makes these data available without charge over the Internet as shapefiles that users can download for use with geographic information system (GIS) software. Accompanying these data for each state and its counties are two versions of the essential metadata: one an extensive, detailed document following the Federal Geographic Data Committee (FGDC) model, the other a one-page summary. There also is a database that describes each change, provides the FIPS codes and complementary ID codes for all states and counties, and gives references to the authorities for every county change. A set of supplementary documents includes chronologies of changes, county areas in square miles for each version of every county, and a bibliography of the laws, maps, and other materials used to compile the boundary changes.