A project of the William M. Scholl Center for American History and Culture, the Atlas of Historical County Boundaries is a powerful historical research and reference tool in electronic form. The Atlas presents in maps and text complete data about the creation and all subsequent changes 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. Funding for the project was provided by the National Endowment for the Humanities and support from numerous private individuals and foundations.
Published in 2010, updated in 2012