Historical GIS

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.

Search for over 50,000 maps available online from the Library of Congress.

The National Historical Geographic Information System (NHGIS) provides easy access to summary tables and time series of population, housing, agriculture, and economic data, along with GIS-compatible mapping files, for years from 1790 through the present and for all levels of U.S. census geography, including states, counties, tracts, and blocks.