About the Project

The Atlas of Historical County Boundaries successfully completed the project of documenting boundary changes in all 50 states in June 2010. The national data files and animations were contributed in 2012.

Project Staff

What Is the Atlas?

A project of the William M. Scholl Center for American History and Culture at The Newberry Library in Chicago, 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 (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.

What makes this Atlas stand out?

A dozen features distinguish the volumes and files of this atlas from other compilations.

  1. All boundary changes in states and counties-unrivaled historical and geographic coverage.
  2. Non-county areas-never before compiled or mapped.
  3. Attachments to operational counties (non-county areas and unorganized counties)-never before compiled or mapped.
  4. Separate map or polygon for every different county configuration-clarity and ease of use.
  5. Based on original research in primary sources-unlike most reference works.
  6. Primary sources cited for every change-unmatched documentation.
  7. Information organized by both date and county-unmatched flexibility.
  8. Locator maps for all county maps-show each county's location within its state.
  9. Area (sq. mi.) for each county configuration-available nowhere else.
  10. Polygons available in two formats: shapefiles and KMZ-broad applicability.
  11. Supplementary bibliography, chronologies, and commentary-unusually complete and thorough data presentation.
  12. Short and Long metadata documents for each state dataset-convenience and completeness.

Digital Products

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.


The Atlas is organized state by state, the obvious approach for institutions like counties that are the direct creations of the states. In addition to files for each of the fifty states, there are separate files for the District of Columbia and Dakota Territory: the District was divided into its own counties until near the end of the nineteenth century, and, whereas the transformation of other territories into states seldom involved more than a change of name, Dakota Territory was unusually complicated and deserved special treatment.


The Atlas is designed to be as comprehensive as possible, leaving no gaps in either space or time. The historical scope covers every day, starting in the early 1600s and extending through the end of the year 2000. Geographically, the range for each state includes all the territory within its bounds in 2000, regardless of what government created or altered a county there, plus any other territory that may have been within the state's jurisdiction at an earlier time.

Importance of Counties

In 2009 U.S. counties and their equivalents (parishes in Louisiana, census districts in Alaska, and independent cities in Maryland, Missouri, Nevada, and Virginia) numbered over 3,000 and embraced within their bounds every part of the fifty states. Counties are important because nearly every aspect of American life can be described, analyzed, and illuminated through data gathered and organized by county or available in county records-and because their boundaries changed often. Although there is no universal standard for county operations-the county's role is smallest in New England, larger in the Middle Atlantic and North Central states, and greatest in the South and West-they share many functions and in every state have been essential. Starting in the colonial period, county functions expanded from legal proceedings and law enforcement to probating wills, recording deeds, and providing courts for civil actions. The recording of marriages, births, and deaths was a natural addition, and eventually much of the work of census taking was organized around the county.

In the twenty-first century the common method of mapping censuses for large areas continues to be the aggregation of statistics at the county level. Most counties also were centers for the organization and training of the militia, and counties acquired many of the functions of local government, including welfare administration, road and bridge maintenance, and property assessment and tax collection. Counties were the obvious geographical units for organizing representation in most colonial, territorial, and state legislatures and for building congressional districts. In the nineteenth century counties became the grassroots centers for political parties. Since World War II, the counties in Connecticut and Rhode Island, and half of those in Massachusetts, have ceased most or all operations and serve chiefly as geographic units for the collection and analysis of economic, political, and social data.


Few counties today have their original configurations. As the non-Indian population grew and spread across the continent, territories and states created new counties and changed those already in existence. The average number of changes in size, shape, or location per American county is between four and five; some counties were changed more than two dozen times. Most boundary changes were alterations of the lines between existing counties, not the results of creating new counties from old ones.

With very few exceptions, the authority to create counties and to change them has been lodged in the colonial, territorial, and state legislatures. The question of why legislators changed counties is beyond the scope of the Atlas, but it is obvious that the motives were numerous and ranged from helping constituents and local officials (e.g., arranging boundaries to follow land survey lines for the convenience of tax collectors and landowners) to the most blatant gerrymandering.

History of the Atlas

The Atlas was conceived in 1975 after historians working on the Atlas of Early American History (1976) at the Newberry Library in Chicago discovered the nearly complete lack of reliable maps of American counties in the revolutionary and early national periods. The U.S. Historical County Boundary Data File Project was launched in 1976 at the Newberry to fill that void in the historical literature by creating a cartographic database of county boundaries for the period from 1788 to 1980. Principal funding was provided by a grant from the National Endowment for the Humanities, an independent federal agency, with additional support from private individuals and foundations and the Newberry, which served as sponsor and headquarters. The choice of an electronic product was based upon a desire to adopt the most economical mapmaking practices-gains in efficiency over manual practices was a theme emphasized by proponents of the then new cartographic technology-and to demonstrate the applicability of that technology to historical cartography. The cartographic laboratory at the University of Wisconsin, Madison, performed the digital cartography. As the first project of its type, the Newberry undertaking necessarily had a strong experimental quality; it was, in effect, an early version of the current Atlas.

Once news of the project spread, many potential users asked that the data also be published in the traditional form of books because few of them had access to the facilities needed to utilize a cartographic database. By late 1982, when the project concluded, staff had compiled data on the evolution of county boundaries in fourteen states during the nineteenth and twentieth centuries. The results were disseminated in five volumes published by G. K. Hall, the Historical Atlas and Chronology of County Boundaries, 1788-1980 (1984), and in a cartographic database, County Boundaries of Selected United States Territories/States, 1790-1980 (ICPSR 9025), deposited with the Inter-University Consortium for Political and Social Research (ICPSR) in Ann Arbor.

The current Atlas was launched in 1987 to complete the work that had commenced in the 1970s, to provide reliable and accessible data on historical county changes for the entire nation. The earlier work had indicated that the research could be successfully extended into the colonial period, so the scope was enlarged, and some technical changes were made in methodology (e.g., the new project would deal with boundary changes as a series of polygons rather than as coded line segments that were the mechanism in the first project) to facilitate data handling and proofing. Nonetheless, the successful outcome of the earlier project set the initial production goals of this Atlas; that is to disseminate the data in two forms, a traditional multi-volume book and a cartographic database. All work, from historical compilation through computerized mapmaking, was concentrated at the Newberry. As in the first undertaking, the National Endowment for the Humanities provided the principal funding, the Newberry served as sponsor and home base, and private individuals and foundations contributed significant additional support.

From the beginning, the strategy was to organize the operation into two stages. First, publish the printed volumes as the data for each state and its counties were compiled, a process that would take several years to complete the country, and, second, defer the cartographic database until the entire nation had been compiled and published. The computer work would be sure to benefit from improvements in electronic mapmaking since the start of the project, and all states and counties could be digitized together. In the event, that original strategy was undone by the unexpectedly rapid advances in the applications of computers to traditional print publication, to cartography-especially geographic information systems (GIS)-and their effect on the markets for printed atlases and for cartographic databases; all together those developments pushed the Atlas project into the production of a digital cartographic product much earlier than anticipated. The net result is that the original plan for the Atlas has been realized in the form of a cartographic database covering all states and counties and available at this Website, plus nineteen printed volumes covering the historical county boundaries of twenty-four states and the District of Columbia. A list of those books and related publications follows.